# Homework Help: Coefficient of Variation

1. Sep 5, 2009

### Darsh

1. The problem statement, all variables and given/known data

I'm stuck trying to find the coefficient of variation of this calculation: 18.97(+/-0.04) + 0.0025(+/-0.0001) + 2.29(+/- 0.08)= 21.2625. The numbers in parenthesis are the standard deviations for each value.

2. Relevant equations

3. The attempt at a solution

I found the overall standard deviation for the equation but now I don't know what to do to go farther. I worked some example problems with the answers in the back of the book and I got close to the correct answer on all three of them by dividing the overall standard deviation by the sum of the problem. However, I don't think this is correct and my book has no examples of finding the CV of a problem like this. Any help would be appreciated!

2. Sep 6, 2009

### HallsofIvy

Think of it this way: if every individual "measurement" were at its largest exteme, we would have 18.97+0.04 + 0.0025+ 0.0001 + 2.29+ 0.08= 21.2625+ (0.04+ 0.0001+ 0.08)= 21.2625+ 0.1201. If each were at it smallest extreme we would have 18.97- 0.04+ 0.0025- 0.001+ 2.29- 0.08= 221.2625- 0.1201.

$18.97\pm 0.04+ 0.0025\pm 0.0001+ 2.29\pm 0.08= 21.2525\pm 0.1201$.