Question

An automated teller machine at a local bank is stocked with $10 and $20 bills. When a customer withdraws $40 from the machine, it dispenses either two $20 bills or four $10 bills. If two customers withdraw $40 each, how many outcomes are possible? Draw a tree diagram for this experiment.

Answer 1

There are 4 possibilities

Explanation

Each customer has 2 ways to receive the money. For each way, the other customer has 2 option, giving a total of 2*2 = 4. Here are the possibilities, separating in 2 different cases.

Case 1: customer 1 withdraws 2 $20 bills

option 1.1: customer 1 withdraws 2 $20 bills AND customer 2 withdraws 2 $20 bills

option 1.2: customer 1 withdraws 2 $20 bills AND customer 2 withdraws 4 $10 bills

Case 2: customer 1 withdraws 4 $10 bills

option 2.1: customer 1 withdraws 4 $10 bills AND customer 2 withdraws 2 $20 bills

option 2.2: customer 1 withdraws 4 $10 bills AND customer 2 withdraws 4 $10 bills

options 1.1, 1.2, 2.1 and 2.2 give us a total of four ways for the customers to retrieve thier money.