Question

There are 10 buses running between two towns X and Y. In how many ways can a man go from X to Y and return by a different bus?

Answer 1

The man can go from X to Y in 10 ways and as he is not to return by the same bus that he took while going, corresponding to each of the 10 ways of going, there are 9 ways of returning. Hence the total number of ways in which he can go to Y and be back is 10 × 9 = 90.