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.