# Random variables (probability)

1. Oct 30, 2015

### TheMathNoob

1. The problem statement, all variables and given/known data
I have the joint cdf of two random variables X and Y and they ask me to find the cdf of just Y. I know that you just take the limit of the cdf as x->infinity, but I am just wondering if you can also do this by calculating the joint pdf and then the marginal of Y and then from the marginal of Y, the cdf of Y.

2. Relevant equations

3. The attempt at a solution

2. Oct 30, 2015

### Ray Vickson

Yes, sometimes that is how it must be done. However, in your case that would be doing it the hard way, since taking the $x \to \infty$ limit is easier.

3. Oct 30, 2015

### TheMathNoob

Thank you!!!!, I was so worried about that one in the test.