1. A building 1 1 has two people entering the elevator. Assuming that the probability of each of them leaving from the second floor on each floor is equal, what is the probability of two people leaving on different floors?

A: Everyone has 10 possibilities ~ * * Yes 10 2 = 100 possibilities.

According to the principle of opposing events: when A B is an opposing event, P(A)= 1-P(B).

There are 10 1 = 10 possibilities when two people get off the elevator at the same time.

So p (b) =1-1100 = 9/10.

2. Two ships, A and B, are heading for a dock where they can't berth at the same time, and it is impossible for them to reach the dock in one day and night. If the berthing time of A is 1h, and the berthing time of B is 2h, find the probability that either of them does not need to wait for the wharf to be vacant.

Answer: Each ship has 12 possibilities ~ * * There are 12 possibilities 2 = 144 possibilities.

According to the principle of opposing events: when A B is an opposing event, P(A)= 1-P(B).

The possibility of two ships arriving at the dock at the same time is122 * a12 = 66 * 2 =132 (one ship stops for two hours ~ one ship stops for one hour and then queues for two hours).

So p (b) =1-132/144 =112.