A, B and C are three cities. There are 5 routes from A to B and 3 routes from B to C. How many different routes are there from A to C via B?
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.