# Thread: Joint cdf problem

1. ## Joint cdf problem

Hi,

I have been given that

f(x,y) = 1.8 - y , 0 < y < < 1

i am trying to find P(X˂Y│Y= 0.5) , E[X│Y>0.5] but i dont know how to set it up.

Any help would be really appreciated.

2. Originally Posted by Number Cruncher 20
Hi,

I have been given that

f(x,y) = 1.8 - y , 0 < y < < 1

i am trying to find P(X˂Y│Y= 0.5) [snip]
Get f(x | y) from this thread: http://www.mathhelpforum.com/math-he...-question.html

by substituting the rule for f(x, y). Then substitute y = 1/2 to get f(x | y = 1/2).

Then $\displaystyle \Pr(X < Y | Y = 1/2) = \int_{x = -1}^{x = 1/2} f(x \,| \, y = 1/2 ) \, dx$.

But given the careless mistakes I've made in two threads related to this question (forgetting about -1 < x < 0), you might want to check this carefully.