Chapter 15.3, Problem 20P

Some transistors of two different kinds (call them $N$ and $P$) are stored in two boxes. You know that there are 6 N ’s in one box and that 2 N’s and 3 P’s got mixed in the other box, but you don’t know which box is which. You select a box and a transistor from it at random and find that it is an N; what is the probability that it came from the box with the 6 N’s? From the other box? If another transistor is picked from the same box as the first, what is the probability that it is also an N?