one of, so the answer is13·124441525.Example.What is the probability that in a poker hand we get exactly 3 of a kind (and he other two cardsare of different ranks)?Answer.The probability of 3 aces, 1 king and 1 queen is434141525. We have 13 choices forthe rank we have 3 of and122choices for the other two ranks, so the answer is13122434141525.Example.In a class of 30 people, what is the probability everyone has a different birthday?(We assumeeach day is equally likely.)Answer.Let the first person have a birthday on some day. The probability that the second person has adifferent birthday will be364365. The probability that the third person has a different birthday from the firsttwo people is363365. So the answer is1-364365363365· · ·336365.Example.Suppose 10 people put a key into a hat and then withdraw one randomly. What is the probabilityat least one person gets his/her own key?Answer.IfEiis the event that theith person gets his/her own key, we want
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