# Variance question

• Dec 4th 2011, 01:37 PM
FelixHelix
Variance question
Hi - I'm stuck on this question:

Given the following sample of three measurements,

10.0 15.2 17.2
what value must be added to the sample to make a new sample having double the variance of these three measurements?

I know the formula for the sample variance but have no idea of how to calculate the new added value....

Any help would be greatly appreciated.

F
• Dec 4th 2011, 06:48 PM
mr fantastic
Re: Variance question
Quote:

Originally Posted by FelixHelix
Hi - I'm stuck on this question:

Given the following sample of three measurements,

10.0 15.2 17.2
what value must be added to the sample to make a new sample having double the variance of these three measurements?

I know the formula for the sample variance but have no idea of how to calculate the new added value....

Any help would be greatly appreciated.

F

Calculate the variance of 10.0 15.2 17.2. Call the number a.

Calculate the variance of 10.0 15.2 17.2 x. Call the result b. It will have x in it.

Solve b = 2a for x.