A local downtown arts and crafts shop found from past observation that 20% of the people who enter the shop actually buy something. Three potential customers enter the shop.
a. How many outcomes are possible for whether the clerk makes a sale to each customer? Construct a tree diagram to show the possible outcomes. (Let Y = sale, N = no sale.)
b. Find the probability of at least one sale to the three customers.
c. What did your calculations assume in part b? Describe a situation in which that assumption would be unrealistic.