







The number of standard deviations 
20140615 

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. 





Sample Standard deviation 
20110316 

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. 





Standard Deviation from a Proportion 
20100608 

silvestre pose la question : A large company finds that approximately 17% of all purchases are returned for credit. If the company sells 100,000 different items this year, about how many items will be returned. Find the Standard Deviation. Janice Cotcher lui répond. 





Standard deviation 
20091027 

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. 





Zscore 
20090325 

Barb pose la question : I am having trouble finding information on a z score and the conversion to the number of standard deviations a z value can be away from the mean.
What exactly does that mean and what am I looking for?
Help Please. Harley Weston lui répond. 





Sigma in a normal distribution 
20081118 

Justin pose la question : Suppose the random variable Y can be described by a normal curve with
Mu=40. For what value of the standard deviation is
P(20 less than or equal to Y less than or equal to 60) = 0.50
Justin Harley Weston lui répond. 





Finding the Raw Score for a Mean of 0 and Standard Deviation of 1 
20081002 

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. 





Expected value and standard deviation 
20080319 

Patrick pose la question : Heres a question i cant figure out:
a small airline company has only three flights per day. The number of
delayed flights per day is regarded as a random variable, and I'm
supposed to calculate the expected
value and standard deviation of the number of delays.
the probability distribution looks like:
No. of Delays: 0 1 2 3
Prob. of delay: 05. 0.3 .1 .1 Harley Weston lui répond. 





Mean and standard deviation 
20071210 

Jamie pose la question : Let n be any odd whole number.
a) Which has the greater mean: the odd whole numbers from 1 to n, or the even whole numbers from 2 to n1?
b) Which has the greater standard deviation: the odd whole numbers from 1 to n, or the even whole numbers from 2 to n1? Penny Nom lui répond. 





A ttest 
20071120 

Rachel pose la question : I am wanting to use the ttest 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 ttest cannot be used because the ftest can't be calculated. If so is there an alternative test? Harley Weston lui répond. 





Standard deviation 
20071120 

Shahzada pose la question : when and why we use standard deviation in Data analysis? Harley Weston lui répond. 





Grouped data 
20071008 

Nimra pose la question : The following sets of data represent the distributions of
house prices in the northeast and southwest of a country.
Random samples of 100 houses were selected in each region.
(a) Calculate the mean, median and standard deviation for Harley Weston lui répond. 





Standard deviation 
20070905 

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. 





Standard deviation 
20070901 

Pat pose la question : I have looked over your math question and mines is not there. for a binomiial distribution with parmeter n and p, the mean is np and the standard deviation is np(1p). I understand how to get the np but not understanding how to get the (1p). For example np=(40)(0.48)(10.48)=3.160. How can I get the (10.48) answer please Harley Weston lui répond. 





A statistics example 
20070802 

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. 





Standard Deviation 
20070613 

Adrian pose la question : If you are told that the mean salary of a certain group of workers is $30,000 with a standard deviation of $4000, what proportion of workers earn over $38,000? What proportion of workers earn less than $18,000? Assume the distribution of wages is normal. Stephen La Rocque lui répond. 





Normal distribution 
20070524 

Paula pose la question : Consider a data set that is normally distributed.
The mean of the data set is equal to 10,000.
a.) Suppose that, for this data set, 10,625 has a
"zvalue" = 2.5. Solve for the standard deviation of
the data set.
b.) Solve for the "zvalue" of 9,900. Penny Nom lui répond. 





Incremental standard deviation 
20070428 

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. 





A one pass calculation of standard deviation 
20070319 

Murtaza pose la question : Hi
I searched the listings but couldn't find what i am looking for. I have a dataset and i am allowed only 1 pass through it. At the end of this pass i must have the mean and standard deviation. Calculating the mean is easy as also demonstrated in your listings. I think the same can be done for standard deviation as well. But the doubt that i have is this : Will the calculated standard deviation be sequence dependent ? i.e. if i change the order in which the data items enter the system, will the std deviation also change ??
Thanks in advance
Murtaza Penny Nom lui répond. 





Standard deviation 
20070115 

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. 





Standard deviation 
20061004 

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. 





Absolute Value vs. Standard Deviation ? 
20060424 

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. 





Means of sample means 
20051012 

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. 





A normal distribution problem 
20050808 

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 
20050102 

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. 





A standard deviation test 
20041109 

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 
20040923 

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 quarterhour 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. 





Statistics from grouped data 
20031009 

Rebecca pose la question :
I have to use a suitable computer package (ie. Excel) to work out the mean and standard deviation of the following:
Price Range No of Houses No of Houses
£`000 Area 1 Area 2
45 and under 50 4 5
50 and under 55 7 12
55 and under 60 14 16
60 and under 70 19 18
70 and under 80 8 3
80 and under 100 5 2
I have used excel to work out mean and standard deviation before, but not in a more complicated example like this. Any advice on where to start would be greatly appreciated. Penny Nom lui répond. 





Standard Deviation 
20031007 

Rebecca pose la question :
I have a task to complete, which is to calculate the mean and standard deviation of something. I have done this but am then asked to write a short explanation of my findings.
I know what the mean is about, and I thought I knew what the standard deviation meant too  shows the variation from the mean. However, on a task I completed earlier the feedback I got said 'you need to tell us that it is talking about the middle 66% of the data'  that has thrown me, I don't understand that. Can anyone help me get my head round this??? Penny Nom lui répond. 





Incremental standard deviation 
20030412 

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. 





Variance 
20021029 

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. 





Range of values for standard deviation 
20020322 

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. 





Can the standard deviation ever = 0? 
20020216 

Karen pose la question : If given a class of 30 people who take a test with a mean of 80. Can the standard deviation ever = 0? If so, why? Penny Nom lui répond. 





Ciefficient of variation 
20010923 

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. 





Standard deviation 
20010922 

Doug pose la question : I was wondering if anybody knows who the founder of standard deviation was? Penny Nom lui répond. 





Comparing means and standard deviations 
20010711 

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. 





Sigma 
20010331 

A student pose la question : What does the Sigma symbol mean in mathematics? Penny Nom lui répond. 





Sample variance 
20000416 

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 n1 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. 





Absolute value 
19991229 

Alex Waller pose la question : What are some practical applications for absolute value? Harley Weston lui répond. 





Estimating the population mean 
19991113 

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. 





Standard Deviation 
19990711 

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. 





Mean and Standard Deviation 
19980422 

Kit pose la question : i have a problem of maths. i think the level of the question is secondary. question: Find the mean and the standard deviation of the numbers:1, 3, 4, 5, 7. i hope u solve this question. thank you so much! Harley Weston lui répond. 

