题干

两个警察抓两个小偷,目击者说:两个小偷分别躲藏在六个房间中的两间,但不知道他们到底躲藏在哪两间。而如果警察冲进了无人的房间,那么小偷就会趁机逃跑。如果两个警察随机地冲进两个房间抓小偷,(1)至少能抓获一个小偷的概率是多少?(2)两个小偷全部抓获的概率是多少?请简单说明理由.

上一题 下一题 0.0难度 选择题 更新时间:2020-02-13 04:48:50

答案(点此获取答案解析)

(1)设房间号为1、2、3、4、5、6,其中假设两个小偷分别躲藏1、2,任意取两个,共有15种等可能的结果数:1、 2;1,3;1,4;1,5;1,6;2,3;2,4;2,5;2,6;3,4;3,5;3,6;4,5;4,6;5,6;其中至少能抓获一个小偷占9 种,所以至少能抓获一个小偷的概率=.
(2)两个小偷全部抓获的结果数占1种,即1,2,所以两个小偷

同类题2

    When I was growing up in America, I was ashamed of my mother's Chinese English. Because of her English, she was often treated unfairly. People in department stores, at banks, and at restaurants did not take her seriously, pretended(假装) not to understand her, or even acted as if they did not hear her.
    My mother has realized the disadvantages of her English as well. When I was fifteen, she used to have me call people on phone to pretend I was she. I was forced to ask for information or even to yell at people who had been rude to her. One time I had to call her stockbroker(股票经纪人). I said in a voice that was not very convincing, “This is Mrs. Tan.” And my mother was standing beside me, whispering loudly, “Why he doesn't send me the check. It's already two weeks late.”
    And then, in perfect English I said: “I'm getting rather anxious .You agreed to send the check two weeks ago, but it hasn’t arrived.” Then she talked more loudly. “What does he want? I’ll come to New York and say it in front of his boss.” And so I turned to the stockbroker again, “I can't accept any more excuses. If I don’t receive the check immediately, I have to speak to your manager when I am in New York next week.”
    The next week we ended up in New York. While I was sitting there red-faced, my mother, the real Mrs. Tan, was shouting to his boss in her broken English. When I was a teenager, my mother’s broken English embarrassed (使困窘) me. But now, I see it differently. To me, my mother’s English is perfectly clear, perfectly natural. It is my mother tongue. Her language, as I hear it, is clear and direct. It was the language that helped me form the way I saw things, expressed ideas, and made sense of the world.