Question 953794
4 bus lines between a and b.
3 bus lines between b and c.


the number of possible combinations between a and c going through b are 4 * 3 = 12.


if you're talking about round trip, he has 12 possible ways to get there and 12 possible ways to get back, so the total possible ways is 12 * 12 = 144.


if he doesn't want to take the same route back, then:


possible ways to get there is 4 * 3 = 12


possible ways to get back is 3 * 2 = 6


total possible ways is 12 * 6 = 72.


possible ways to get back is 3 * 2 because he can't use the same route coming back then he did going.  he therefore has to take one possible route away from the b to a section and 1 possible route away from the c to b section.


that results in 3 possible ways from b to a and 2 possible ways from c to b.