Not sure how to go about this one..
Johnís wallet contains two $20-bills, one $10-dollar bill, and three $5-dollar bills. On this particular summer day, Johnís friend Eddy is visiting and Eddyís wallet contains one $20, three $10s, and one $5. Both wallets look the same and are sitting together on the table. When little Jenny hears the ice cream truck coming she asks her dad John if she can have
some money for an ice cream. He tells her she can go grab a bill out of his wallet. She runs to the table, randomly grabs a bill out of one of the wallets, buys an ice cream for $2 and then returns the change to one of the wallets (not remembering which one she took the money
from). A tree diagram would be useful here!
(a) What is the probability that Eddy goes home with more money than he came with?
(b) What is the probability Eddy still has his $20-bill when he leaves?
(c) If the change Jenny returns with is more than $5, what is the probability she took the money from the correct wallet?