Problem: A man can commute either by train or by bus. If he goes to work on the train in the morning, he comes home on the bus in the afternoon; and if he comes home in the afternoon on the train, he took the bus in the morning. During days the man rode the train times and rode the bus times in the morning and times in the afternoon. Find .
Answer Choices:
A.
B.
C.
D.
E. not enough information given to solve the problem
Solution:
The total number of trips is , so and .