An urn contains 4 pink marbles and 4 green marbles. Two marbles are drawn at random. What is the probability that the first one is pink and the second one is

For the first pick, there are 8 marbles, four of each color, meaning that there is a 50/50 chance of getting either one. The second pull is the same as the first (because there is replacement) meaning both of the pulls have a 1 in 2 chance of happening. You multiply both results because they need to coincide. This gives you a 1 in 4 chance of this happening.