Say we have two people waiting for Facebook to approve their marketplace posts. Let Y the the sum of their independent exponential wait times in hours where each wait time rate is 1/2 (1 post is approved every half hour). It will help to recall that there is a special relationship between Exponential and gamma random variables. The sum of n Exp( ) random variables is a gamma (n, ) random variable. Then what is P(Y1) ?.