Question

find the error% of f in the equation
f=uv/u+v

Answer 1

$df= \frac{df}{du}$Δx$+ \frac{df}{dv}$Δv

I remember this formula. Differentiate your function with respect to u and v separately. 
Here you differentiate your function partially. 
 You may need Δu and Δv... 
Error %=$\frac{df}{f}*100$