# Urgent Help Needed in Percentage Error Calculation

1. Oct 1, 2009

### kd001

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

The quantity Z is a function of 2 variables A and B.
Z=A^4/B
A=1.253 (error0.005) B=20.7 (error 0.2)
Calculate percentage error in Z.

2. Relevant equations

I have the relevant error expressions
if Z=A/B (errorZ/Z)^2 = (errorA/A)^2 + (errorB/B)^2

if Z=A^n errorZ/Z=n.errorA/A

3. The attempt at a solution

I don't know how to combine the different standard error expressions.

Thanks for any help.

2. Oct 1, 2009

### Donaldos

$$Z=\frac{A^4}{B}$$

so in this case

$$\frac{\Delta Z}{Z}=\frac{\Delta \left(A^4\right)}{A^4}+\frac{\Delta B}{B}$$

and since

we have

$$\frac{\Delta \left(A^4\right)}{A^4}=4\frac{\Delta A}{A}$$