问题 问答题

一个袋子中有5个球,编号为1,2,3,4,5,同时从中任取3个,以x表示取出的3个球中的最大号码,求随机变量X的概率分布.

答案

参考答案:

依题意,随机变量X只能取值3,4,5;日P{X=3}=

所以X的概率分布为

阅读理解

阅读下文并回答问题。

Some time ago, an old businessman had a large store in Boston. He wanted a boy to work for him, and he put an advertisement in the newspaper. The next morning, many boys came to the old man’s office, asking for the job.

There was a post(柱子)by his desk, and there was a nail(钉子)in it. He took a walking-stick and said, “Everyone has three chances. If anyone can hit the nail on the head with this stick more than once, I will give him the job. ”

The boy thought it was very easy. They all tried, but nobody could make it. So the old man said, “I’m sorry I can’t take any of you. ” And they left.

He kept the advertisement in the papers, and the next morning many more boys came, and among them he saw a thin boy who had been there the day before. The boy hit the nail successfully for three times. The old man felt surprised and asked how he did that.

“Yes,” said the boy, “I failed yesterday, but I thought that if I kept on trying a while, I could do it. So I went home and practiced hitting a nail with a stick till I could do it, and I got up very early this morning, and tried again. ”

The old man said, “You are the boy for me,” and gave him the job. Whatever the boy had to do, he tried to do his best. It was not very long before he became the best clerk in the store.

小题1:Did the thin boy get the job at last?

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小题2:What did the old man have in Boston?

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小题3:Where did the boy practice hitting a nail?

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