题目内容
设有10张奖劵，其中8张为2元，2张为5元，现从中无放回地随机抽取3张，则得奖金额（单位：元）的数学期望是
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1.It isn't fair for the police to ticket acar only minutes after the parking meter runsout.
2.The first parking meters were installed in Oklahoma City, Oklahoma, in July of1935.
3.ThefirstwordsspokenbyThomasEdisonintoaphonograph,hisinvention, were "Mary had a littlelamb."
4.The voting machine was a more important invention than thephonograph.
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