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Two spinners 2018-08-13
Atina pose la question :
A spinner has four equal sectors and a number is written on each sector; 1, 2, 3 and 4. A two-digit number is formed by spinning two times. The number on the first spinning makes the first digit and the number on the second spinning makes the second digit. For example, 2 on the first spinning and 1 on the second spinning make the number 21.
(a) Give the sample space S for the experiment.
(b) Consider the following events : E = odd number; F = number smaller than 35; G = prime number. Give the subset of outcomes in S that defines each of the events E, F, and G.
(c) Describe the following events in terms of E, F, and G and find the probabilities for the events.
• getting an even integer less than 35.
• getting an odd number or an prime.
• getting an even number greater than or equal to 35 that is a prime number.
• an odd number smaller than 35 that is not a prime number.
(d) Are E and F mutually exclusive events? Give a reason for your answer.

Penny Nom lui répond.
Percentage of water in a soil sample 2012-03-01
avi pose la question :
what i need is the formula in getting the percentage from gram. situation:
i need to know how many percent will i declare in getting the moisture of a soil sample i weighed 2,000 grams of soil before i dried it out in the oven, after few hours the recovery of the dried out soil is 1,700 grams. How many percent will be the water content? kindly send me a formula in computing this.
thank u very much!

Penny Nom lui répond.
Sample size 2010-03-29
Rae pose la question :
What sample size was needed to obtain an error range of 2% if the following statement was made? "75% of the workers support the proposed benefit package. These results are considered accurate to within + or - 2%, 18 out of 20 times. This seems like a straight forward question but I'm getting it wrong. Could you please help me out even just the set up would be appreciated so I can see if that's where I'm going wrong. Thanks
Harley Weston lui répond.
Sample variance 2010-01-25
shodhan pose la question :
A series of 100 measurements of a physical quantity have been made that show a random fluctions characterized by a sample variance of 2% of teh mean value. If the series is lengthed to 1000 measurements made under the same conditions, estimates the sample variance of the larger set of data.
Robert Dawson lui répond.
The distribution of sample sums 2008-11-21
Mark pose la question :
For large samples, the sample sum (Σ x) has an approximately normal distribution.
The mean of the sample sum is n*μ and standard deviation is (σ*√n). The distribution of savings per account for savings and loan institution has a mean equal to $750 and a standard deviation equal to $25. For a sample of 50 such accounts, find the probability that the sum in the 50 accounts exceeds $38,000.

Penny Nom lui répond.
Sample variance: inches to centimeters 2008-09-22
Anita pose la question :
The average height of a sample of basketball players is 6 feet, 2 inches or 74 inches. The standard deviation of this sample of players is 4 inches. If each person's height were to be multiplied by 2.54, what would be the value of the resulting sample variance?
Harley Weston lui répond.
z-score 2008-07-02
Candace pose la question :
If a normal-shaped distribution has a mean of 80 and a standard deviation of 15 what is the z-score for M=84 for a sample of n=25 scores. Is this sample mean in the middle 95% of the distribution?
Harley Weston lui répond.
The distribution of sample means 2008-07-02
crystal pose la question :
A population forms a normal distribution with a mean of 75 and a standard deviation of 20. How do I sketch the distribution of sample means for samples of n= 100?
Harley Weston 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.
Sample size 2007-07-17
Nurse pose la question :
If a population has standard deviation 20, what is = the minimum sample size to be 95% confident that the error should be = accurate to within 4?
Harley Weston lui répond.
Find the sample size needed 2007-05-13
Mini pose la question :
Find the sample size needed to be 98% confident thata marketing survey on the proportion of shoppers who use the internet for holiday shopping is accurate within a margin of error of 0.02. Assume that the conditions for a binomial distribution are met, and that a current estimate for a sample proportion does not exist.
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.
Choosing a bicycle 2007-03-28
Jackie pose la question :
A specific brand of bike comes in two frames, for males or females. Each frame comes in a choice of two colors, red and blue, and with a choice of three seats, soft, medium, and hard.
a) Use the counting principle to determine the number of different arrangements of bicycles that are possible.
b) Construct a tree diagram illustrating all the different arrangements of bicycles that are possible.
c) List the sample space.

Penny Nom 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.
Two word problems 2005-11-14
Jennifer pose la question :

1. Every other person on a school's parent advisory committee is surveyed to determine how many people support passage of a school bond to build a new elementary school. Is this a good sample? Why or why not?

2.What is the difference in elevation between the highest point in California,Mount Whitney,which towers 4421 meters above sea level, the lowest point in California,Death Valley, which lies 86 meters below sea level?


Harley Weston lui répond.
A random sample 2005-10-16
Stu pose la question :
If I have a set of data points (14 to be exact)of unknown pedigree from a large population, what tests can I apply to see if they constitute a random sample from the large population?
Andrei Volodin and Penny Nom lui répond.
Means of sample means 2005-10-12
Fareeha pose la question :
A population consists of six numbers 1,2,3,4,5,6
a) How many different samples of two numbers can be selected with replacement? and list them.
b) Calculate the mean and standard deviation of the population
b2) Calculate the mean and standard deviation of the mean of the samples.
c) Find the standard error of your estimated mean in question b2 and compare with the estimated standard deviation in b2.

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.
X bar 2003-11-04
mary pose la question :
Remind me what this means:

    _    
    X 

Andrei Volodin 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.
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.
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.
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.
 
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