Math Help - Conditional density function

1. Conditional density function

A number x is an element [0, infinity] is selected so as to have an exponential distribution with parameter alpha >0, that is fx(X) = alpha* e^-alpha*x for all x>=0 and zero otherwise. Once X = x is chosen, a second number Y is select so that it is uniformly distributed on the interval [ x, x+ beta] for soe constant B > 0.

Calculate the conditional density function of f[y|x=x](y)?
Ok so i knwo the formula for this is fx,y(x,y)/fy(y) but i have no idea where to get the y part....

The answer is given by 1/beta....

2. I'd bet that you really want to find X|Y
since it looks like we know that Y|X is uniform (X,X+B)

This should be $f_{Y|X}(y|X=x)={1\over B}$ when $x\le y\le x+ B$.