Question

Wrong formula for standard deviation?
I attached a picture. Please help.

Answer 1

I think that it should be n-1 NOT n(n-1) in the numerator. Am I right?

Answer 2

there are 2 versions of the formula

Answer 3

The one is with "n" and with "n-1"?

Answer 4

But I couldn't find a formula with n(n-1). But she said that it is OK. ???

Answer 5

one version is\[\frac{n\sum (x^2)-(\sum x)^2}{n(n-1)}\]

the other version, the one i am used to using is\[\frac{\sum (x-\bar x)^2}{n-1}\]

Answer 6

OK but then she did not include the "n" in the denominator.

Answer 7

I understand what you say, but the formula I attached is wrong

Answer 8

it does appear that youve merged 2 different version in what you posted

Answer 9

She wrote the version that you like using, but included n(n-1) not n-1

Answer 10

I think that is the case. I think the teacher mixed the 2 verison.

Answer 11

if she wrote it, then most likely it was a transcription error.

Answer 12

I also prefer to use the n-1 verison

Answer 13

this site does the algebra to form it from one to the other :)

http://mathforum.org/library/drmath/view/71724.html

Answer 14

Thank you !!!