Suzie June and Grace enjoy eating ice cream at the local ice

Suzie, June and Grace enjoy eating ice cream at the local ice cream shop. Their favorite topping is mini M&Ms. Suzie puts only one scoop on her ice cream but June and Grace each put two scoops. On a given day the probability that each girl comes in by themselves is 0.1. Much of the time all three girls come in with probability of 0.4. Sometimes just June and Grace come together, probability of 0.05. Sometimes June and Suzie come in together, probability 0.1. And sometimes none of the girls can come because their mothers think they’ve had too much sugar (probability .15). What is the expected number of scoops of mini M&Ms the store will need to have for these three girls on a given day?

Solution

Expected number of scoops of mini M&Ms the store will need to have for these three girls on a given day = 1(1/3)+2(2/3)=5/3=2.