Answer : Given: 5 routes from A to B and 3 routes from B to C. To find: number of different routes from A to C via B.

Let E1 be the event : 5 routes from A to B Let E2 be the event : 3 routes from B to C

Since going from A to C via B is only possible if both the events E1 and E2 occur simultaneously.

So there are 5 × 3 =15 different routes from A to C via B.