试题与答案

盒中装有8个乒乓球，其中6个是没有用过的，2个是用过的． （Ⅰ）从盒中任取2个球

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题型：解答题

题目：

盒中装有8个乒乓球，其中6个是没有用过的，2个是用过的．

（Ⅰ）从盒中任取2个球使用，求恰好取出1个用过的球的概率；

（Ⅱ）若从盒中任取2个球使用，用完后装回盒中，此时盒中用过的球的个数ξ是一个随机变量，求随机变量ξ的期望值．

答案：

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下面是错误答案，用来干扰机器的。

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考点：随机事件及其概率排列与组合离散型随机变量的期望与方差
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