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	A stem-and-leaf plot with decimals		2020-04-02
		Renee pose la question : I am an AP Statistics student who is reviewing for the exam. On one of my review worksheets, we have to create a stem-and-leaf plot for values with 2 decimal places (i.e. 9.14, 8.14, 8.74, 8.77, 9.26, 8.1, 6.13, 3.1, 9.13, 7.26, and 4.74). How would I make the stem-and-leaf plot for this? I've already searched your database and nothing popped up. If you could help me, that would be great. Thank you! Penny Nom lui répond.
	The binomial distribution		2019-10-01
		PY pose la question : An on-line game called ‘Shop Quiz’ is held by an e-commerce platform, from Monday to Friday every week. It consists of 8 multiple choice questions (MCQ) and each question has four options (A, B, C, D). Only one option is the correct answer. People who are able to correctly answer all 8 questions are winners and will be awarded a number of on-line shopping credits. Let X represent the number of questions that a person can answer correctly in a ‘Shop Quiz’. 1) Explain why Binomial distribution might NOT be a suitable distribution for the random variable X. Mr. Saul likes playing the quiz, however, he is afraid that he might not have the necessary knowledge to answer the quiz questions. (The quiz questions cover a variety of topics including science, history, entertainment, sports and geography, etc.) Therefore, he tries to win the game by simply guessing the answers to each question. Penny Nom lui répond.
	Matched pairs		2017-12-13
		Lin pose la question : PLEASE HELP WITH THIS VERY DIFFICULT STATISTICS QUESTION(the process would really help) Imagine you and your 4 study group partners are interested in whether all those hours you spent together working on statistics problems for midterm exam 2 actually helped your group's performance on that exam relative to its performance on the first midterm exam. Suppose the first and second midterm grades were as follows: Is there sufficient evidence (at a = :05) to conclude that the group performed better on midterm 2? Please provide all your calculations.   midterm 1 midterm 2 A 25 28 B 20 19 C 15 21 D 16 25 E 20 22 Penny Nom lui répond.
	A pie chart		2016-12-05
		vickie pose la question : Determine the central angle needed to form a pie chart for the following housing characteristic data: 63% owner occupied, 27% renter occupied, and 10% vacant Penny Nom lui répond.
	The number of standard deviations		2014-06-15
		Dawn pose la question : Suppose that, at a certain college, the average weight of all male students is 160 pounds with a standard deviation of 30 pounds. A certain male student weighs 145 pounds. Determine how many SD's his weight is above or below average. Penny Nom lui répond.
	Cumulative Frequency Math Question		2013-03-20
		Primadonna pose la question : Hi, Please help me solve this question. Thank you so much. The cumulative frequency table below shows the length of time that 30 students spent text messaging on a weekend. Minutes Used Cumulative Frequency 31-40 2 31-50 5 31-60 10 31-70 19 31-80 30 Which 10-minute interval contains the first quartile? (1) 31–40 (2) 41–50 (3) 51–60 (4) 61–70 Penny Nom lui répond.
	The range in grouped data		2012-08-27
		maria pose la question : Question from maria, a student: how to find range from group data.?i know that it is the difference between largest and smallest value.but confuse to find range of group data e.g class interval frequency 0------5 6 5------10 7 10------15 9 15------20 4 Robert Dawson lui répond.
	A normal distribution problem		2012-05-13
		Alysia pose la question : The scores on a test taken by 1000 students are normally distributed with a mean of 66 and standard of deviation of 12. If the college wishes only the top 8% of people to get an A, what would the cutoff score be for the A's? Penny Nom lui répond.
	A pie chart		2012-05-01
		muhammad pose la question : How can i construct a pie chart on the following of the combunation of students:- Sos 50, Crs 25, Eng 100, Iss 75, Geo 150, Hist 10 Penny Nom lui répond.
	Expected value		2012-02-24
		Lara pose la question : A life insurance company sells a $250,000 1-year term life insurance policy to a 20-year-old male for $350. According to the National Vital Statistics Report the probability that the male survives the year is 0.998734. Compute and interpret the expected value of this policy to the insurance company. I'm very confused on how to do this. I assume x is the profit the insurance company makes in the year of $350 but beyond that I don't know what to do. Thanks. Penny Nom lui répond.
	The same mean but different ranges		2012-01-14
		swathi pose la question : Frank and Frances work out at their local gym. the mean of their workout times is the same: 48 min. however, the range of Frank's workout times is 7 min, while the range of Frances'sworkout times is 16 min. explain how this is possible. Penny Nom lui répond.
	The average age of 300 cars		2011-11-22
		Jason pose la question : I have 300 used cars built from 1970 to 1980, I would like to know the average age by total volume. If I provide the qty built per year, can I determine the average age of the lot (300) by total volume? Total built 50 56 30 10 30 25 64 9 12 14 Year built 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 Thanks Penny Nom lui répond.
	Sample Standard deviation		2011-03-16
		Iris pose la question : Help please: me on this type of math problem I can get through step one after that I get lost. Maybe you can explain it to me in a easier way to get the correct results. I have read the examples, but I am still lost cannot move on until the next practice until I get this one Sample standard deviation The following are distances (in miles) traveled to the workplace by employees of a certain computer company. 15,29,32 28 18 28 Find the standard deviation of this sample of distances. Round your answer to at least two decimal places. Penny Nom lui répond.
	A normal distribution problem		2010-12-02
		Racquel pose la question : I am stuck on this question. I am not sure if using the z score will help me get the answer I need. Here is the question? The average length of time per week that students at this university spend on homework is normally distributed with a mean of 18 hours and a standard deviation of 3 hours. If Diane spends more time on homework each week than 75% of students, what is the minimum time she must spend? Penny Nom lui répond.
	t scores, z scores, standard scores and percentile ranks		2010-11-25
		Imogen pose la question : I have an assignment that requires me to calculate the t scores, z scores, standard scores and percentile ranks of 3 children on a vocab task. I am struggling with how to calculate the correct T-scores for the children, my tutor has said that the sample has a mean of 50 and standard deviation of 10. So on a z- score of 2.0 (2 SD's from the mean) it would be 50 + 10+10 = T score of 70. However the Z- scores i have are not whole numbers so I am struggling with it, i have one that is 1.27 , another that is 0.47 and the last one is 0.80. If you could help me on how to calculate these to get T scores that would be great. Thanks. Robert Dawson lui répond.
	Standard deviation		2009-10-27
		Reggie pose la question : After you have computed the standard deviation of a set of 40 scores, you discover that the lowest score is in error and should be even lower. Will correcting this error affect the standard deviation? Penny Nom lui répond.
	Airline overbooking		2009-09-03
		Nikita pose la question : An airline company knows that 8% of it's passengers will not show up for their scheduled flights. A plane has 175 seats. a) What is the probability that 10 passengers or fewer will not show up? b) What is the probability that 10 to15 passengers will not show up? c)What is the probability that exactly 10 passengers will not show up? d) What is the probability that more than 19 passengers will not show up? Robert Dawson lui répond.
	Normal Distribution		2009-09-02
		Nikita pose la question : Scores on a college exam are known to be normally distributed with a standard deviation of 20. If the top 3% have scores in excess of 200, what is the mean score? Robert Dawson lui répond.
	A normal distribution problem		2009-03-21
		EDGAR pose la question : to qualify for security officers training recruits are tested for stress tolerance. The scores are normally distributed with mean of 62 and a standard deviation of 8. a.) If only the top 15% of recruits are selected, find the cutoff score b.) If a candidate is rendomly selected, what is the probability that his or her socre is at least 55? Harley Weston lui répond.
	Probability		2009-03-12
		jude pose la question : ) Assuming that the heights of boys in high school basketball are normally distributed with a mean of 70 inches and a std dev. of 2.5 inches, how many boys in a group of 100 are expected to be 75 inches tall. 2) Past records from a bank show that the probability of being approved in the written application for hire is 0.63. Then the probability of being approved by the interview committee is 0.85, given that the candidate has been approved on the written application. What is the probability that a person will be approved on both the written application and the interview? Robert Dawson lui répond.
	The variance		2009-02-09
		Ashley pose la question : what is the varinace of these scoress 53,67,43,54,58,54,47,35,45,56,45,47,54 Harley Weston lui répond.
	The range of a set of numbers		2008-11-19
		krista pose la question : hi, i was working on a math problem for homework and it asked me to find the range out of these numbers: 1,15,16,16,19,25,27,28,28, can you help me? Penny Nom lui répond.
	Finding the Raw Score for a Mean of 0 and Standard Deviation of 1		2008-10-02
		Anita pose la question : A variable Y has a distribution of mean of Y =80 and standard deviation of Y=36. Find the values of A and B for transforming y*=A +BY so that mean of y* =0 and standard deviation of y*=1. Janice Cotcher lui répond.
	Reading a Histogram		2008-09-05
		Bea pose la question : From a histogram only, can you find the frequency per each increment of an interval? Janice Cotcher lui répond.
	Alpha level		2008-07-23
		anonymous pose la question : What is the advantage of using an alpha level of .01 versus a level of .05, What is the disadvantage of using a smaller alpha level? Janice Cotcher lui répond.
	A pre-employment evaluation		2008-02-06
		lisa pose la question : An employer gives a pre-employment evaluation to a large group of applicants. The scores are normally distributed with a mean of 154 and a standard deviation of 21. The employer wants to interview only those applicants who score in the top 15%. What should the cut off score be for the interviews? Harley Weston lui répond.
	The standard normal distribution		2007-12-29
		GEORGE pose la question : Statistics texts state that in a normal distribution, 1 standard deviation covers 68%, 2SD 95% 3SD 99.7%. However, on looking at the tables for normal curve areas, the percentage for a z value of 1 is 84.13. 68 % of values are covered at a z value of 0.47. The discrepancies exist even for other values but are smaller. So why is the rule of thumb so different from the Table for Normal Curve areas? Harley Weston lui répond.
	A decision based on data		2007-12-04
		manny pose la question : You have administered a standardized test of manual dexterity to two groups of 10 semi skilled workers. One of these two groups of workers will be employed by you to work in a warehouse with many fragile items. The higher the manual dexterity of a worker the less likelihood that worker will break significant inventory. Because of a unique contract you must hire all 10 employees from one of the two groups and none of the employees from the other. You must decide which group to choose. Choose at least two measures of central tendency and at least one measure of dispersion for each group and use those to make your choice. Be sure to justify your choice with at least one page of discussion and analysis. Penny Nom lui répond.
	A t-test		2007-11-20
		Rachel pose la question : I am wanting to use the t-test to find if temperature over a period of 5 days was significantly different to the mean temperature for that time of year. So i want to compare expected temps to actual temps. The problem is that because the expected temperature is the same for the 5 days it gives me a standard deviation of zero. Does this mean the t-test cannot be used because the f-test can't be calculated. If so is there an alternative test? Harley Weston lui répond.
	p-values and t-distributions		2007-11-13
		Don pose la question : I have a t-test statistic of 1.28 and a degree of freedom of 6. I know the p-value is .248 I cannot figure out how to calculate that value. I have used software to get it but I want to know how to calculate it using the t-distribution table. Harley Weston lui répond.
	Stem & Leaf Plots		2007-11-02
		Jen pose la question : Trying to help my Gr.4 son with his math and i am a little lost here are the stem and leaf plots.. Stem Leaves 4          02 3          1226699 2          011255789 1          33357899 Stem Leaves 2          00011111223334455 1          range566788899 Question - How are the ranges for the stem & leaf plots different ? Penny Nom lui répond.
	Sample variance and population variance		2007-09-22
		Willy pose la question : I have a question in sample variance and population my name is Willy the question in the attached file... Harley Weston lui répond.
	Standard deviation		2007-09-05
		Ethan pose la question : Okay I have a question about standard deviation. Can you tell me a five number set of data that will have a standard deviation f zero and how you know that? Stephen la Rocque lui répond.
	A statistics example		2007-08-02
		Claudia pose la question : A particular employee arrives to work some time between 8:00 am - 8:30 am. Based on past experience the Company has determined that the employee is equally likely to arrive at any time between 8:00 am - 8:30 am. On average, what time does the employee arrive? What is the standard deviation of the time at which the employee arrives? Find the probability that the employee arrives exactly at 8:12 am? Find the probability that the employee arrives between 8:20 am - 8:25 am? Har lui répond.
	The difference between two dice		2007-06-02
		smiley pose la question : Two standards dice are rolled. Determine the probability that the difference between the two numbers on the dice is 2 Penny Nom lui répond.
	Types of variances		2007-05-08
		Latoay pose la question : my teacher asked me to name two type of vairiance. i feel the answer is population and simple variance but i'm not sure. thank you Stephen La Rocque lui répond.
	Incremental standard deviation		2007-04-28
		Murtaza pose la question : Hi In relation my question asked earlier, i would first like to thank you for the prompt reply. But it has not answered my query yet. Let me frame the problem again. I have a mean value for N data items. (note that i know N but i donot know the distinct N data item values) Now the (N+1)th data item comes in and i calculate the new mean. (incremental method for that is simple). How do i calculate the new standard deviation. The formula you gave me requires me to read the data items once and at the end of the pass i will have have the standard deviation. But i need the STDDEV values at intermediate stages as well. Is it possible ? Murtaza Penny Nom lui répond.
	All samples of size 3		2007-04-19
		Liz pose la question : Consider the population of the first seven integers: 1, 2, 3, 4, 5, 6, and 7; N=7. For this population, mean = 2 and standard deviation = 2. a. How many samples of size three can be extracted from this population (sampling without replacement)? b. Form the complete set of samples of size three and for each sample, compute the sample mean and median. Penny Nom lui répond.
	A box-and-whisker plot with no whiskers		2007-04-18
		Paula pose la question : Is it possible for a box-and-whisker plot to have no whiskers? 3 whiskers? Penny Nom lui répond.
	A hypothesis test		2007-04-09
		Katrina pose la question : I have already tried to do this problem but im having a very had time with it. Can you please help me. Glamour Magazine sponsored a survey of 2500 prospective brides and found that 60% of them spent less than $750 on their wedding gown. Use a 0.01 significance level to test the claim that less than 62% of brides spend less than $750 on their wedding gown. How are the results affected if it is learned that the responses were obtained from magazine readers who decided to respond to the survey through an Internet Web site? Penny Nom lui répond.
	A missing observation		2007-04-02
		destinee pose la question : please help me my problem is 5,11,19,3,15,17,5,n find n given the following info.range:16 mode:5 median:8 mean:10 what the heck is the answer Penny Nom lui répond.
	Acceptance sampling		2007-03-29
		Katrina pose la question : The Medassist Pharmaceutical Company recieves large shipments of asprin tablets and uses this acceptance sampling plan: Randomly select and test 24 tablets, then accept the whole batch if there is only one or none that doesnt meet the required specifications. If a particular shipment of thousands of asprin tablets actually has a 4% rate of defects, what is the probability that this whole shipment will be accepted? Penny Nom lui répond.
	Skewness		2007-03-16
		Lyndsey pose la question : How do I calculate the skewness of a set of data? Penny Nom lui répond.
	Range in statistics		2007-02-28
		Steve pose la question : I was wondering if the range is considered as a positive or negative number, or does it ignore such indications? Penny Nom lui répond.
	Standard deviation		2007-01-15
		Kayleigh pose la question : After i have added up all the squared deviations what do i do???, what is meant by "divide by one less than the sample size" Stephen La Rocque lui répond.
	A statistics question		2007-01-07
		Rick pose la question : For many years TV executives used the guideline that 30 percent of the audience were watching each of the prime-time networks and 10 percent were watching cable stations on a weekday night. A random sample of 500 viewers in the Tampa-St Petersburg, Florida, area last Monday night showed that 165 homes were tuned in to the ABC affiliate, 140 to the CBS affiliate, 125 to the NBC affiliate, and the remainder were viewing a cable station. At the 0.05 significance level, can we conclude that the guideline is still reasonable? Penny Nom lui répond.
	Standard deviation		2006-10-04
		Jennifer pose la question : I was wondering how to figure out a standard deviation if you only have the mean of the data and no other information? Stephen La Rocque lui répond.
	The median		2006-09-26
		Sam pose la question : How do you find the median in a group of numbers? Stephen La Rocque and Penny Nom lui répond.
	The coefficient of variation		2006-05-20
		Glenn pose la question : What is the correct formula for coefficient of variation for a binomial distribution? Penny Nom lui répond.
	Absolute Value vs. Standard Deviation ?		2006-04-24
		Sonia pose la question : Why we don't just take the average of the absolute value of difference scores (use the mean deviation) to describe variability instead of calculating the standard deviation? Claude Tardif lui répond.
	A manufacturer of cotton pins		2006-03-20
		Nirmal pose la question : A manufacturer of cotton pins knows that 5% of his products are defective. If he sells cotton pins in boxes of 100 and guarantees that not more than 10 pins will be defective, what is the approximate probability that a box will have the guaranteed quantity? Penny Nom lui répond.
	Outliers in a box and whisker plot		2006-02-19
		A student pose la question : i need help on determining if their is an outlier...i know how to find the median and the lower quartile and the upper quartile..but i don't understand about the outliers....please tell me if their is an outlier in this problem....the numbers are...63,88,89,89,95,98,99,99,100,100 Penny Nom lui répond.
	Another normal distribution problem		2006-02-18
		Mary pose la question : Assume that blood pressure readings are normally distributed with a mean of 120 and standard deviation of 8. A researcher wishes to select people for a study but wants to exclude the top and bottom 10 percent. What would be the upper & lower readings to qualify people to participate in the study? Penny Nom lui répond.
	Broken-line graphs and histograms		2006-02-16
		George pose la question : 1. What is the main difference between a broken-line graph and a histogram? Both represent continuous variables. 2. What is the correct way to read a multiplication array: x-axis first and then y-axis, other way around or it doesn't matter? Penny Nom lui répond.
	A normal distribution problem		2006-02-15
		Mary pose la question : In a certain normal distribution, find the mean when the standard deviation is 5 and 5.48% of the area lies to the left of 78. Penny Nom lui répond.
	The median		2006-01-27
		Wael pose la question : " median"; what does it mean and how do we calculate it? Penny Nom lui répond.
	A confidence interval		2006-01-21
		Jonathan pose la question : I am attempting to calculate how my confidence interval will widen at the 95% confidence level if my response universe increases from 100 to 150 or to 200. There is a universe of 54,000. I take a 5% sample for a test universe of 2,700 If my "yes" universe is 100, at the 95% confidence level, what is my +/- range? (i.e +/- 3? +/-5?) Historically, 6.6% of the 2,700 you say "yes". I am trying to determine how the confidence interval would change if the number of "yes" responders increased to 150 or to 200. Penny Nom lui répond.
	Mean and average		2005-12-22
		Jerry pose la question : This is just a question from a degreed engineer that has a "understanding" problem. please go to http://www.metrika.com/3medical/hemoglobin-m.html At the end of the page they talk about "mean" vrs "average" there does appear to be a difference. What is it? Harley Weston lui répond.
	A sample size estimation		2005-12-03
		Ivonne pose la question : I have to do a research about the behavior of library users. We are going to apply a survey to a population of 1280 students (Management an Economics students) but of course we have to do it to a sample....I need to know the size of my sample. Penny Nom lui répond.
	Coefficient of variation		2005-10-19
		Jan pose la question : I am currently teaching the coefficient of variation and am wondering if there are some guidelines as to the interpretation of this statistic. I understand that it measures the variation in a variable relative to the mean - but what is the cut off for "too much" variation expressed in this way??? Andrei Volodin and Penny Nom lui répond.
	The range of a data set		2005-10-04
		Carmen pose la question : What is the range of this data? 36,64,37,45,53,60. Penny Nom lui répond.
	Sample variance		2005-08-17
		Rosalie pose la question : To give an unbiased estimate of the population variance, the denominator of the sample variance should be (n-1) instead of n. I tried to convince myself by comparing the population variance and sample variance (with denominator n and n-1): Penny Nom lui répond.
	A normal distribution problem		2005-08-08
		Brad pose la question : The life of a toy is normally distributed. Suppose 92.51% of the items lives exceeding 2,160 hours and 3.92% have lives exceeding 17,040 hours. Find the mean and the standard deviation. Penny Nom lui répond.
	Standard deviation		2005-01-02
		Urial pose la question : Find the standard deviation of the given data set To get the best deal for CD dealer, Jessica called eight appliance stores and asked the cast of a specific model. The prices she quoted are listed below. $300, $203, $272, $332, $440, $119, $129,$254 Penny Nom lui répond.
	Computing confidence intervals		2004-11-26
		Christie pose la question : I was given a question with N=100, sample proportion is 0.1- compute the 95% confidence interval for P? I have tried this several ways but do not know how to do without means, standard deviations, standard error of the mean? I asked my teacher and she said I have all the info I need. Can you help???? Penny Nom lui répond.
	A standard deviation test		2004-11-09
		Karen pose la question : How do you compare to see if a sample standard deviation is different than the population standard deviation? I know how to compare means, but not standard deviations. Penny Nom lui répond.
	Incremental variance		2004-09-23
		Carlos pose la question : I must keep statistical data (mean and variance) in 3 granularity levels depending on the age of the data (daily for older than 1 year, hourly for older than 1 month and quarter-hour for older than 1 day). How can I calculate the resulting variance from a set of variances previously calculated supposing I have the count and mean for each member of the set? Andrei Volodin and Penny Nom lui répond.
	Percentiles		2004-08-15
		Gary pose la question : Table 1 Selected percentiles for family income in the US in 1992 1 $1,300 10 $10,200 25 $20,100 50 $36,800 75 $58,100 90 $85,000 99 $151,800 Q. The percentage of families in Table 1 with incomes below $58,100 was about? Penny Nom lui répond.
	A probability question		2004-08-15
		Gary pose la question : In a law school class, the entering students averaged about 160 on the last LSAT; the standard deviation was about 8. The historgram of the lLSAT scores follwed the normal curve reasonable well. Q. About what percentage of the class scored below 166? Q. One student was 0.5 above average on the last LSAT, about what percentage of the students had lower scores than he did? Penny Nom lui répond.
	The p-value		2004-07-25
		Kathy pose la question : Ms. Lisa Monnin is the budget director for the New Process Company. She would like to compare the daily travel expenses for the sales staff and the audit staff. She collected the following sample information. At the .10 significance level, can she conclude that the mean daily expenses are greater for the sales staff than the audit staff? What is the p-value? Having problems finding the p-value & unsure of the formula. Kathy Penny Nom lui répond.
	Chi-Squared		2004-05-05
		Gillian pose la question : OF75 PEOPLE, 43 ARE EXPOSED TO A VIRUS AND BECOME ILL. 11 PEOPLE ARE EXPOSED AND DO NOT BECOME ILL. 3 PEOPLE ARE NOT EXPOSED AND BECOME ILL. 18 PEOPLE ARE NOT EXPOSED AND DO NOT BECOME ILL. THE ATTACK RATE IS 80% FOR THOSE EXPOSED AND 14% FOR THOSE NOT EXPOSED. THE RELATIVE RISK IS 5.7. CAN YOU EXPLAIN TO ME HOW TO CALCULATE A CHI SQUARE TEST FROM THIS. Penny Nom lui répond.
	Replacement times for TV sets?		2004-03-31
		Barb pose la question : Replacement times for TV sets are normally distributed with a mean of 8.2 years and a standard deviation of 1.1 years. Estimate the probability that for 250 randomly selected TV sets, at least 15 of them have replacement times greater than 10.0 years.e Andrei Volodin and Penny Nom lui répond.
	A least squares line		2003-11-09
		Michelle pose la question : Hooke's Law asserts that the magnitude of the force required to hold a spring is a linear function of the extension e of the spring. That is, f = e0 + ke where k and e0 are constants depending only on the spring. The following data was collected for a spring; e: 9 , 11 , 12 , 16 , 19 f : 33 , 38 , 43 , 54 , 61 FIND the least square line f= B0 + B1x approximating this data and use it to approximate k. Penny Nom lui répond.
	X bar		2003-11-04
		mary pose la question : Remind me what this means: _ X Andrei Volodin lui répond.
	Means		2003-10-28
		Abdu pose la question : Question: 80,80,84,85,88,92,97,98 The average of the 8 numbers listed above is 88. Of the following which pair of numbers could be removed from the list without changing the average. A. 80 and 97 B. 80 and 98 C. 84 and 92 D. 84 and 97 E. 85 and 92 Andrei Volodin and Penny Nom lui répond.
	The mean house price		2003-09-10
		Carol pose la question : Question: I have to find the mean from the following example: Price Range £000 No of Houses 55 and under 60 3 60 and under 65 6 65 and under 70 13 70 and under 80 21 80 and under 100 15 100 and under 130 7 130 upwards 1 I know when calculating the mean you use the mid points of the classes, but how does this work for the 130 upwards class? Also, does this still work given the difference in the classes (ie. 1st class is 5, 5th class is 20, etc). Any help to get me started would be greatly appreciated. Penny Nom lui répond.
	E(X + Y) and V(X + Y)		2003-07-10
		Reuben pose la question : I'm a teacher trying to find a way to make some stats work from first principles. The topic is expectation algebra and it is for the top age level in high school. By using a set of data I can show how the mean is the same as the expected value ie 2,2,3,4,4 is 15 / 5 = 3 also, 2x0.4+3x0.2+4x0.4=3. I can also show this to work for the variance in the same style but using Sum(x-mean)2/n and the Var(X) version of squaring x then multiplying by the probability ( all this for random independant samples). Now comes the tricky bit.....when I try to show E(X+Y) = E(X) + E(Y) from setting up two data sets I get it to work only if I add each item from X to each item from Y. However, I can't get it to work for V(X+Y)=V(X) + V(Y) from two sets of data. There must be something missing in my knowledge of how the sets are required to add together or my knowledge of expectation algebra. I am familiar with proofs but still want to show my students that the basic formulae work from groups of data whether done the long way or by use of formulae. Can you help please? Penny Nom lui répond.
	The effectiveness of a drug		2003-04-22
		A student pose la question : A certain drug is found to be effective 80% of the time. Find the probability of successful treatment in two out of four cases. Andrei Volodin lui répond.
	Incremental standard deviation		2003-04-12
		Carlos pose la question : I need to calculate the standard deviation for a group of data, but I don't know in advance what is the mean. Is there a way to adjust the STDV for each datum without keeping all of the previous values? This is needed basicaly for performance, so I won't need to read twice the same data (spend processing time) nor save the previous values (spend memory). Andrei Volodin and Penny Nom lui répond.
	Mean and median		2003-01-04
		Jan pose la question : I have a question re: mean and median. I know what the difference is but just need some clarification on when you would use the mean and when you would use the median. Isn't it the case that with a skewed distribution the average (mean) would be higher or lower than the median, but with a normal distribution they would be very similar values? If you have any examples to help explain this that would be greatly appreciated. I am a teacher (of sorts!) and the person who is asking me the question is actually my boss! Penny Nom lui répond.
	Variance		2002-10-29
		Ade pose la question : I am trying to solve a standard deviation question, I have 30 data points to use, should I group the data before solving for variance or should I just use the raw data. Andrei Volodin lui répond.
	Statistics		2002-10-11
		Ed pose la question : Suppose 25 percent of all U.S. workers belong to a labor union. What is the probability that in a random sample of 100 U.S. workers, at least 20 percent will belong to a labor union? Claude Tardif lui répond.
	Mean, median and mode		2002-09-08
		Ramona pose la question : How do you calculate the mean, median, and mode? what are each of their definitions? Leeanne Boehm lui répond.
	On which assignment did I do better		2002-05-17
		Denise pose la question : I have 2 writing assignments in class. The first assignment, which had a mean of 10 and a standard deviation of 2, I got a score of 12. The second assignment had a mean of 18 and an s.d. of 3, I got a 21. I need to know which assignment did I do better, relative to my classmates? Andrei Volodin lui répond.
	Day care		2002-05-13
		Sonam pose la question : In many familes, both parents work. as a result, there is increasing need for day care. data was collected; and in one year in Canada, approximately 32% of children aged 0 to 11 years were in day care for at least 20h per week. (a) what is the probability, in a random poll of 60 children form the age of 0 to 11, that more than 15 children are in day care at least 20 h per week? nearest tenth of one % ANSWER: P(children are in daycare at least 20h)= 60/60C14 = to the answer (b) what is the probability, in a random pool of 60 children that fewer than 20 are in day care at least 20 h per week? ANSWER: P= 20/60= 33.3% stay in day care for 20h per week, I dont know if these answers are right please help me out. Andrei Volodin lui répond.
	The Dugout, Don's Basement, Cd Corner,...		2002-04-30
		A student pose la question : The Dugout, Don's Basement, Cd Corner, Harry's Deli, Bill's Software, Anne's Footwear, and Joanne's House cleaning. The gift certificates are each in multiples of $5. There is a $100 range in the value of the gift certificates, which start at $25. The mean value of all seven gift certificates is $80, and the median and mode are both $70. The certificate from The Dugout is worth the most and the one from Joanne House cleaning is worth the least. The total value of the gift certificates from CD Corner, Harry's Deli, and Anne's Footwear is $270, but Anne's Footwear certificate is worth $50 more than the one from Harry's Deli. The Cd Corner gift certificate is equivalent to the mean for this group of three. What is the value of the gift certificates from each store? Penny Nom lui répond.
	Range of values for standard deviation		2002-03-22
		Susan pose la question : What is the range of values for standard deviation? Is it between 0 and +3? Is it between +1 and +3? Andrei Volodin lui répond.
	Testing a hypothesis		2002-03-14
		A student pose la question : A large distriutor of cosmetics has kept his outstanding accounts receivable to a mean age of 18 days over the past year. This average is considered a standard by which to measure the efficiency of the credit and collections department. Management wishes to check if receivables in the current month is over standard and will do this at a significance level of 0.50. A random sample of 100 accounts yields an average of 20 days with a standard deviation of 9 days. what should management conclude? Andrei Volodin lui répond.
	The median with ties		2002-02-27
		Marcel pose la question : What, exactly, is the proper way to determine the median of a set of numbers when doubles or triples of a number are part of that set? Do the doubles count as two and the triples three, or does each count only as one toward determining the median. Harley Wston lui répond.
	Linear regression		2002-01-16
		Murray pose la question : If you have a set of coordinates (x[1],y[1]),(x[2],y[2]),...,(x[n],y[n]),find the value of m and b for which SIGMA[from 1 to m=n]AbsoluteValue(y[m]-m*x[m]-b) is at its absolute minimum. Harley Weston lui répond.
	Cinderella clothes		2001-12-11
		A student pose la question : If cinderella clothes, inc. has determined that 0.5% of all incoming phone calls involve complaints, what is the probability that in 200 incoming calls there are more than one complaint? Andrei Volodin lui répond.
	Box and Whisker plots		2001-11-19
		Rod pose la question : In our Prealgebra course, we have been studying Box and Whisker plots. Recently, we learned how to decide whether a data point is an outlier or not. The book (Math Thematics, McDougall Littell) gave a process by which we find the interquartile range, then multiply by 1.5. We add this number to the upper quartile, and any points above this are considered to be outliers. We also subtract the number from the lower quartile for the same effect. My question: where does this 1.5 originate? Is this the standard for locating outliers, or can we choose any number (that seems reasonable, like 2 or 1.8 for example) to multiply with the Interquartile range? If it is a standard, were outliers simply defined via this process, or did statisticians use empirical evidence to suggest that 1.5 is somehow optimal for deciding whether data points are valid or not? Penny Nom lui répond.
	A sample size problem		2001-10-28
		Charles pose la question : The U.S Transportation Dept. will randomly sample traffic reports to estimate the proportion of accidents involving people over the age of 70. The Dept. has no advance estimate of this proportion. how many reports should the dept select to be atleast 97% confident that the estimate is within .01 of the true proportion? Harley Weston lui répond.
	Column doesn't add up to 100%		2001-10-17
		A student pose la question : why don't some tables I'm studying in a column add up to 100%? Example: N=338, but responses to questions asked in survey I'm studying equal of 24.3, 9.8, 43.8, DON'T add up to 100%. I'm assuming that some people surveyed out of the 338 didn't bother responding, but is there another problem related to proportion or ratio being used, but improperly labeled on graph?. Note at bottom of table says: "number in parenthesis are numbers of cases" and 338 was in parentheses. I'm lost. Penny Nom lui répond.
	Ciefficient of variation		2001-09-23
		Carmen pose la question : I have a question from my OAC finite class. I've come across a problem with the coefficient of variation. I have taught my students that there are no units for coefficient of variation and it can be expressed as a percent. So, for example, a set of data with mean of 5 and standard deviation of 100 would have a CV of 5%. But what happens in this situation: the mean is 4meters and the standard deviation is 0.7mm. Is the CV 1.75% or 0.00175% or 0.0175%? I've had some students change leave the units as is, change them both to mm or change them both to meters...so which is it and why? Penny Nom lui répond.
	Margin of error		2001-07-13
		Jim pose la question : If a survey was completed by four different groups of people as indicated below what would the over-all margin of error be for this survey given the fact that the number of people in each group were different? Group # polled Margin of error A. 779 +/- 4% B. 315 +/- 7% C. 323 +/- 6% D. 254 +/- 9% Andrei Volodin lui répond.
	Comparing means and standard deviations		2001-07-11
		Shelly pose la question : Is there a way to compare means and standard deviations that come from different size samples? Is there an equation that can normalize sample size? Andrei Volodin lui répond.
	A confidence interval		2001-06-28
		Murray pose la question : An investigator wants to find out of there are any difference in "skills" between full and part time students. Records show the following: Student Mean Score Std Dev Number ---------- ----------------- ---------- ----------- Full time 83 12 45 Part time 70 15 55 Compute a 95% confidence interval for the difference in mean scores. Andrei Volodin lui répond.
	SPRT		2001-05-24
		A researcher pose la question : I have a medical-pharmaceutical study that says: SPRT (something to do with Secuential and Truncated). Do You know what it means S.P.R.T. and what it is? Ejaz Ahmed and Penny Nom lui répond.
	A confidence interval		2001-04-26
		Kim pose la question : A poll asked 1528 adults if they were in favor of the death penalty, 1238 said yes, find 99% confidence level for percent of all adult who are in favor of the death penalty. Andrei Volodin lui répond.
	Expected value		2001-04-24
		Cindy pose la question : A game consists of rolling a single fair die. If a number great than 4 is rolled you win the number of dollars showing on the die. If any other number is rolled, you receive $1.00. What is the expected value of this game? Andrei Volodin lui répond.
	Leukemia		2001-04-15
		Don pose la question : Assume: Leukemia occurs at an incidence of 1 in 10,000. Benzene is a known carcinogen which causes Leukemia and has been found in toxic levels in the homes of a community of 1200 people. Question: How many cases of Leukemia would be necessary to reject the null hypothesis. That is, to suggest that statistically, the cases are more likely due to benzene exposure rather than chance. Chris Fisher and Penny Nom lui répond.
	Stem-and-leaf plot		2001-03-29
		Kelly pose la question : I'm tutoring my 5th grade nephew, and he needs to correct test questions regarding a stem - and - leaf plot. He left his book at school and I'm not familiar with the term. Can you explain it to me so that I can help him? Penny Nom lui répond.
	What is the difference between Mean and Average?		2000-12-13
		Julie pose la question : What is the difference between Mean and Average? My thinking is the average, is the equal to the sum of all numbers divided by the number of numbers added together. But the mean, I think should be calculated by adding the largest and smallest numbers in the set and them dividing by 2. (which is the point where 1/2 the numbers are higher and 1/2 the numbers are lower) Patrick Maidorn and Penny Nom lui répond.
	Expected number		2000-11-02
		James pose la question : 1)There are 40,25,50 students in the traditional,reformed,and reformed traditional Calculas sections taught by three teachers. On one fine day the three sections congregate together to watch the NOVA video tape on Fermat's Last Theorem. a) A student is randomly selected from he crowed of students.What is the expected number of students in the same section of this student? ****this question which i did not have any idea to do as follow for the part b b) If one of the three teachers is selected at random, what is the expected number of students taught by is teacher? Harley Weston lui répond.
	Mode		2000-09-22
		James Barton pose la question : I have always been told that a mode is the "one" number that appears most in the set of numbers: ex.{1,3,4,6,3,2} the mode is 3. What if you have {1,1,3,4,5,5}is there a mode. I was taught long ago that there is no mode, Not i am having to teach there is two modes. 1 and 5. If this is the case if we have {1,1,2,2,3,3,4,4,5,5} that every number is the mode. True or false. This is being ambigiuous if we say all are the mode. Because no one number is used more than the others. Claue Tardif and Harley Weston lui répond.
	Central Limit Theorem and Law of Large Numbers		2000-06-26
		Jonathan Yam pose la question : The Central limit Theorem states that when sample size tends to infinity, the sample mean will be normally distributed. The Law of Large Number states that when sample size tends to infinity, the sample mean equals to population mean. Is the two statements contradictory? Paul Betts and Harley Weston lui répond.
	Probability and odds		2000-05-05
		Leah pose la question : The chances of rain on friday, saturday, and sunday are 20%, 30%, and 50% respectively. what are the odds it will rain all three days? Harley Weston lui répond.
	An expected value		2000-04-24
		Carl Pride pose la question : Suppose that in a statistics class of size 23, each student has a probability of passing of 73 percent. sample: What is the expected number of students who will pass?? Harley Weston lui répond.
	Sample variance		2000-04-16
		Jonathan Freeman pose la question : I was just reading your article entitled "A Note on Standard Deviation" I'm now teaching a unit on s.d. and my students were wondering why one uses a denominator of n for a population and n-1 for a sample. I saw in your article that this is because "[the quantity] tends to underestimate sigma... and other technical reasons." To which my students again asked... "Why?" Could you please elaborate a bit on the "other technical reasons" perhaps in terms a high school senior (or their teacher...) could understand? Harley Weston lui répond.
	Box and whisker plots		2000-03-09
		Brett Blake pose la question : Do you have any information on Box and whisker graphs? Harley Weston lui répond.
	Bar graphs and histograms		2000-01-11
		Raeluck pose la question : What is the difference between a bar graph and a histogram? Harley Weston lui répond.
	Absolute value		1999-12-29
		Alex Waller pose la question : What are some practical applications for absolute value? Harley Weston lui répond.
	.400 in Baseball		1999-12-15
		Nieve Nielson pose la question : I have several questions to ask about the probability of getting a .400 in baseball: What is the probability of a baseball player hitting a .400 in one game, considering that the hitter is up to bat four times? What is the probability of a baseball player hitting a .400 in a season, considering that there are 100 games in a season? With the first two questions in mind: Considering that baseball has been around for about 100 years, about how many people should hit .400 inthat time? Chris Fisher lui répond.
	Mean, median and mode		1999-12-07
		J William Morning pose la question : Using the data values 2,2,10,6,5, determine the median, mode and mean. Penny Nom lui répond.
	Estimating the population mean		1999-11-13
		John Barekman pose la question : Statitistics: Estimating the population mean when the standard deviation is known: I am not sure which n to use in the formula for the confidence interval equation: x +/- z*(standard deviation/sqrt(n)) If we have data of ten people, and if we have the data of ten sets of ten people each, what is the difference in the n that we use? What is the difference between the standard deviation and the standard error? Are we using the number of sampling means or just the number of samples? Harley Weston lui répond.
	Body part measurements		1999-11-10
		V Bailey pose la question : I am a kindergarten teacher and mother of a 6th grader who wants to do a science project on the correlations of body part measurements. We heard this on the radio and it sparked our interest, but now I cannot find any information about it. Examples are: your height is supposed to equal the distance from fingertip to fingertip when your arms are outstretched. Your foot size is supposed to equal the distance from your wrist to your elbow. Please help me find more information on this topic. Penny Nom lui répond.
	Linear models		1999-11-09
		Helen Moreno pose la question : What is a linear model? Harley Weston lui répond.
	Predictions		1999-09-22
		Joesph Dana pose la question : How do u find the results of an unbiased sample of 100 students that are shown on the table. For example the school has a total of 1,150 students prdict how many students would chose cereal(46) pancakes(15) eggs(20) and sandwich(19) Haeley Weston lui répond.
	Stem and Leaf Plot		1999-09-14
		Jeanette Sovick pose la question : My 5th grade son brought home a math paper, the title of which reads, Reading Stem-and-Leaf Plots...can you explain this so I can explain it to him...There is no book, his teacher just sent this practice sheet home for him to complete and I have no clue! Penny Nom lui répond.
	Standard Deviation		1999-07-11
		Anthony Fama pose la question : I have seen several answers to this question: If one standard deviation represents 68% of the population, what does two, three, four and five sigma [std deviation] represent? As stated, I have seen several different answers and thus, the impetus for my question. Harley Weston lui répond.
	Probability and Statistics		1999-03-25
		Karrie Waller pose la question : Hi my name is Karrie and I am an elementary ed. student at Florida State University in Tallahassee, Florida. I am doing a report on how children learn probability and statistics. I am having trouble locating information that will tell me specifically how students learn. I am wondering if you can answer this question for me or direct me in the right direction. Jack LeSage lui répond.
	Fitting a Curve		1999-01-19
		Kirk pose la question : Hello my name is Kirk from Scarborough, Ontario. I have been out of a formal education system for thirty years. I program microcontrollers in my spare time. I have built a temperature sensing device ready to go but, thermistors are very non-linear. I do know that there is a way to calculate the input condition of the thermistor and display the correct temperature in degrees C. I am sending a file to show my progression so far. Harley Weston lui répond.
	Random		1998-09-15
		Hugh Ballantyne pose la question : I am an occasional teacher. Here is my question: Does the word "random" have a technical meaning in mathematics? Harley Weston lui répond.
	Graph Distortion		1998-02-19
		Dana Steffan pose la question : What exactly is graph distortion? I have to explain it for a project and I can't seem to find anything on it. Penny Nom lui répond.
	Histograms.		1997-09-26
		David Wilson pose la question : I need some help to teach my daughter the functions and the techniques involved in solving histograms. She is in the 7th grade and is in a prealgebra class. She was give these as homework, however there is no section in her book explaining what a histogram is or how to solve them. Thanks! Penny Nom lui répond.
	The normal distribution.		1997-03-21
		Donna D.Hall pose la question : I am looking for a proof for the normal distribution. I suppose "proof" was not a good choice of words. What I am looking for is a way to "derive" the normal distribution in simple terms so that the most average teenager can see the logic. Can you help me? Harley Weston lui répond.
	What is the variance of the difference of two binomials?		1996-02-08
		Chris Johnson pose la question : My co-workers and I have come up with different estimates of the z-statistic, and are in particular disagreement over the calculation of Variance for this problem. I am trying to find out, with a five percent level of significance, whether the new form yields a higher rate of return than the old form. Any thoughts, comments, or solutions? Harley Weston lui répond.

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