The joint probability density of random variables X and Y is given by
f(x,y)=e^-(x+y) , 0<= x <= 無限 , 0 <= y <= 無限,
Find (a) p[X<Y] (b) p[X<a],where n > 0.
(a)小題小弟已算出是1/2
(b)小題則…搞不懂它的意思

請機率高手指點一下…