# Homework Help: Error Propagation

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1. Sep 27, 2015

### newbe318

1. The problem statement, all variables and given/known data
Suppose you measure three numbers as follows:

2. Relevant equations
x= 200. +-2.
y= 50. +-2.
z= 40. +-2.

where the three uncertainties are independent and random. Use step-by-step propagation to find the quantity
q= x/(y-z) with its uncertainty.
3. The attempt at a solution
I do not know what to do. The only thing I am thinking of doing is taking the derivatives of the func., q= x/(y-z), with respect to x, y, and z, .... and .... that's it. I'm stuck. Help, please?

2. Sep 27, 2015

### Student100

How is error propagated in the (y-z) part? That will produce some new uncertainty a, which you then propagate for x/a. How far have you actually gotten?

3. Sep 27, 2015

### newbe318

I didn't get very far.
I skipped that problem and continued with my other homework problems.

4. Sep 27, 2015

### Student100

Do you know how error is propagated in subtraction?

5. Sep 27, 2015

### newbe318

You add them?

6. Sep 28, 2015

### Student100

You add the sum of the uncertainties squared, then take the square root. Is it apparent why?

So what's the uncertainty of a?

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