What is the probability that he pulls out a sock that is white, returns it to the drawer, and pulls out another sock that is white?

Question

A boy has 25 socks in his top dresser drawer.  7 are black, 10 are white, and 8 are grey.  The drawer is above the top of his head, so he cannot see what color a sock is until he reaches in and pulls it out. 

Answer 1

Let event A be picking out white sock first time

Let event B be picking out white sock second time

Since sampling with replacement, event A and event B are independent and probability of both occurring is the product of each individually occurring, which is the same, 10/25 = 2/5, both times.

So probability of picking white sock both times = 2/5 * 2/5 = 4/25