作者tyougennki (everyday is happy!)
看板GRE_Verbal
标题[讨论] 数学题目
时间Thu Aug 16 18:52:20 2007
Q:
In an insurance company, each policy has a paper record and an electric record.
For those policy having incorrect paper record, 60% also having incorrect
electric record; For those policy having incorrect electric record, 75% also
having electric(我猜这边应该是paper..)record, 3% of all policies have both
incorrect paper and incorrect electric records. If we randomly pick out one
policy, what's the probabilty that the one having both correct paper and
correct electric records?
这题我看到的解题方式是
如把总数设X
incorrect paper record设Y
incorrect electric record设Z
会有以下的连立方程式出来
(1)X*Y*60%=3%*X
(2)X*Z*75%=3%*X
从以上导出Y=5% Z=4%
两这之间至少有一个错误的百分比为5%+4%-3%=6%
所以正确答案是
94%
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我不太懂的是(1)和(2)的X和Y为何要相乘
她这题的问题应该是说整份纸面记录的里面有60%有电子纪录错误
电子纪录里有75%的书面记录有错
看不太懂这是什麽意思...
还是我的读解有错呢??
请高手帮忙指点Orz....
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※ 编辑: tyougennki 来自: 203.70.110.210 (08/16 18:52)
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