Two boys have identical piggy banks The older boy has 18 qua

Two boys have identical piggy banks. The older boy has 18 quarters and 12 dimes in his; the younger boy, 2 quarters and 8 dimes. One day the two banks get mixed up. You pick up a bank at randomand shake it until a coin comes out. What is the probability that you get a quarter? Note that there are 20 quarters and 20 dimes in all.

Solution

Probability = 20C1 / 40C1 = 0.5