Probability density function of equivalent resistance in parallel resistors

[darthhath]

I have a problem where there are two resistors in parallel and I need to find the equivalent resistance. R1 = X and R2 = Y, and X and Y are independent random variables, uniform over the range of 100-120.

If R equivalent = Z = XY/X+Y, what is probability density function of Z?

 

[willib]

Z also equals 1/(1/x +1/y) hope this helps..

 

[darthhath]

I know how to find Z when it equals X+Y by using convolution, but I don't know how to do it in this case. How do I find the inverse of X or Y?