题目内容
某商场开展购物抽奖活动，抽奖箱中有4个标号分别为1、2、3、4的质地、大小相同的小球，顾客任意摸取一个小球，然后放回，再摸取一个小球，若两次摸出的数字之和为“8”是一等奖，数字之和为“6”是二等奖，数字之和为其它数字则是三等奖，请分别求出顾客抽中一、二、三等奖的概率.
解：抽中一等奖的概率为
，························································ 3分
抽中二等奖的概率为
，····································································· 5分
抽中三等奖的概率为
． 8分
，························································ 3分抽中二等奖的概率为
，····································································· 5分抽中三等奖的概率为
． 8分 略
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100，
100；方差是
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