91影视

Given a family of two children (assume boys and girls equally likely, that is, probability for each), what is the probability 1/2 that both are boys? That at least one is a girl? Given that at least one is a girl, what is the probability that both are girls? Given that the first two are girls, what is the probability that an expected third child will be a boy?

A card is selected from a shuffled deck. What is the probability that it is either a king or a club? That it is both a king and a club?

A letter is selected at random from the alphabet. What is the probability that it is one of the letters in the word 鈥減robability?鈥� What is the probability that it occurs in the first half of the alphabet? What is the probability that it is a letter after x?

You are trying to find instrument A in a laboratory. Unfortunately, someone has put both instruments A and another kind (which we shall call B) away in identical unmarked boxes mixed at random on a shelf. You know that the laboratory has 3 A鈥檚 and 7 B鈥檚. If you take down one box, what is the probability that you get an A? If it is a B and you put it on the table and take down another box, what is the probability that you get an A this time?