试题与答案

在一副扑克牌中，拿出红桃2、红桃3、红桃4、红桃5四张牌，小明从中随机摸出一张记

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题型：解答题

题目：

在一副扑克牌中，拿出红桃2、红桃3、红桃4、红桃5四张牌，小明从中随机摸出一张记下牌面上的数字为x，然后放回洗匀，再由小华随机摸出一张，记下牌面上的数字为y，组成一对数（x，y）。

（1）用列表法或树状图表示出（x，y）的所有可能出现的结果；

（2）求小明、小华各摸一次扑克牌所确定的一对数是方程x+y=5的解的概率。

答案：

解：（1）画树状图，如图：

（2）∵x=2，y=3或x=3，y=2是方程x+y=5的解，

∴概率P（x+y=5）=。

考点：列举法求概率
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     Just then a boy put up his hand and said, "Miss Li, you told us that water has no color and no smell.

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     "I am sorry, children," said the teacher."Our water is getting dirtier and dirtier. That's a problem. "

1. The students were having their _______ class.

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B. Chinese

C. chemistry                  

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A. water                    

B. air

C. earth                      

D. weather

3. A boy said, "The water in the river behind my house is always      ____  .

A. whit e                    

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D. clear

4. Most of the children _       __  the boy.

A. agreed with            

B. wrote to

C. heard from              

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