[請教] 數學題目
看板GRE (GRE入學考試)作者tyougennki (everyday is happy!)時間17年前 (2007/08/16 18:52)推噓0(0推 0噓 0→)留言0則, 0人參與討論串1/2 (看更多)
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(我猜這邊應該是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?
這題我看到的解題方式是
如把總數設X
incorrect paper record設Y
incorrect electric record設Z
會有以下的連立方程式出來
(1)X*Y*60%=3%*X
(2)X*Z*75%=3%*X
從以上導出Y=5% Z=4%
兩這之間至少有一個錯誤的百分比為5%+4%-3%=6%
所以正確答案是
94%
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我不太懂的是(1)和(2)的X和Y為何要相乘
她這題的問題應該是說整份紙面記錄的裡面有60%有電子紀錄錯誤
電子紀錄裡有75%的書面記錄有錯
看不太懂這是什麼意思...
還是我的讀解有錯呢??
請高手幫忙指點Orz....
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※ 編輯: tyougennki 來自: 203.70.110.210 (08/16 18:52)
※ 編輯: tyougennki 來自: 203.70.110.210 (08/16 18:55)
※ 編輯: tyougennki 來自: 203.70.110.210 (08/16 18:58)
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