# mean and standard deviation

• Sep 12th 2007, 05:16 PM
chocolatelover
mean and standard deviation
Hi everyone,

I'm trying to explain why the following conclusion is not valid:

A student notes that the Wednesday class had a larger mean homework score than the Tuesday class and then concludes that the standard deviation must be larger in the Wednesday class.

I know that this can't be true because the two are not dependent on each other, but I tried an example and it seems to be true. When the mean was 8 the standard deviation was 1.30 and when the mean was 240/21 the standard deviation was 12.021.

Can someone give me a hint on this, please?

Thank you
• Sep 12th 2007, 07:31 PM
CaptainBlack
Quote:

Originally Posted by chocolatelover
Hi everyone,

I'm trying to explain why the following conclusion is not valid:

A student notes that the Wednesday class had a larger mean homework score than the Tuesday class and then concludes that the standard deviation must be larger in the Wednesday class.

Wed homework scores: 70, 71, 75
Tue homework scores: 70, 35, 17

RonL