Hi guys, I have a question about joint probability.

The problem is:

The joint probability fxn for the continuous random variables X and Y is given by

f(x,y) = c, 0<=x<=y<=1 (c is a constant),

= 0 otherwise

Find the probability that X + Y < 1.

I was thinking that I'm supposed to take the double integral, from 0 to 1/2 and from x to 1-x, of (c)dydx, since x < y, but I'm not too sure.

Any help would be greatly appreciated!