imc

Question

A box contains 5 chips, numbered 1, 2, 3, 4, and 5. Chips are drawn randomly one at a time without replacement until the sum of the values drawn exceeds 4. What is the probability that 3 draws are required?

Accepted Answer

Notice that the only four ways such that 3 draws are required are 1,2; 1,3; 2,1; and 3,1. Notice that each of those cases has a 15 14 chance, so the answer is 15 14 4 = 15, or 15.