SOLUTION: looking for the standard deviation for these numbers. 38 45 47 47 48 50 50 52 58 62 62 63 64 68 70 72 72 72 72 74 78 79 80 80 82 84 88 90 94 9

Algebra ->  Probability-and-statistics -> SOLUTION: looking for the standard deviation for these numbers. 38 45 47 47 48 50 50 52 58 62 62 63 64 68 70 72 72 72 72 74 78 79 80 80 82 84 88 90 94 9      Log On


   

Question 125696: looking for the standard deviation for these numbers.
38 45 47 47 48 50 50 52 58 62

62 63 64 68 70 72 72 72 72 74

78 79 80 80 82 84 88 90 94 99
First I add all numbers to find the mean. 2040/30=68
here is where I get lost.
I subtract the lowest number from the mean. 38-68=-30
and subtract the largest number from the mean. 99-68=31
I square them and add them together and that is where I get stuck.
(-30*-30)=900 (31*31)=961. 900+961=1861 Now am I supposed to divide by 2 or 30

I am a little confused.
Darrin
Found 2 solutions by stanbon, solver91311:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
See the example on the following site:
http://richardbowles.tripod.com/maths/normdist/calc_sd1.htm
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Cheers,
Stan H.

Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!
You need to subtract the mean from EACH of the 30 data points.
Then square EACH of the differences.
Then add up all of the squared differences.
Divide this sum of squares by the number of data points minus 1 (29) (this is because you are doing a sample of a population).
Take the square root of the quotient.

sigma=sqrt%28%281%2F%28N-1%29%29%2Asum%28%28x%5Bi%5D-x%5Bbar%5D%29%5E2%2Ci=1%2CN%29%29 x%5Bbar%5D is the mean of your sample.

Drop me a line and I'll send you a spreadsheet that shows all of the calculations.