Question 13
There are four bus routes between A and B; and three bus routes between B and C. A man can travel round-trip in number of ways by bus from A to C via B. If he does not want to use a bus route more than once, in how many ways can he make round trip?
**Editorial note for this self-study exercise:** Each listed route can be used in either direction; reversing direction does not make it a new route. The trip is A to B to C, then C to B to A, with no detours.
**Editorial note for this self-study exercise:** Each listed route can be used in either direction; reversing direction does not make it a new route. The trip is A to B to C, then C to B to A, with no detours.