【费费数学】第六部分（1-5）

祈晴坊主

以下是引用gsluo在2003-5-29 16:31:00的发言：
NO3 的（2）为什么可以？

NO 5能不能再详细些

就是用1去乘啊
列个式子就很清楚了

利用那个不等式  a+b≥2根号ab

CasualWalk

3) 因為N<5﹐所以兩個解濾掉一個。

joywzy

以下是引用祈晴坊主在2003-5-28 13:54:00的发言：
第五题不用挨个算的
因为1/a+1/b+1/c+1/d+1/e=1
把它去乘a+b+c+d+e
则=5+a/b+b/a+a/c+c/a……
>5+2*根号（a/b*b/a)+……
＝5+2+2+2+2+2=15

能不能说慢一点,没明白啊.谢谢.

joywzy

以下是引用Zeros在2003-5-26 4:01:00的发言：
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1、In an insurance company, each policy has a paper record or an electric record, or both of them. 60 percent of the policies having incorrect paper record have incorrect electric record and 75 percent of the policies having incorrect electric record have incorrect paper record. 3 percent of all the policies have both incorrect paper and incorrect electric records. If we randomly pick out one policy, what is the probability that it is one having both correct paper and correct electric record?

  

这一题能不能详细说说?谢谢.

祈晴坊主

首先，用最重要的公式就是那个不等式：a+b≥（a+b)^1/2

那么原题中1/a+1/b+1/c+1/d+1/e=1
用它去乘a+b+c+d+e

=1+b/a+c/a+d/a+e/a+1……（后面四个依次类推）
=5+b/a+a/b+c/a+a/c+……
≥5+2*genhao(b/a*a/b) ~~~~（依次类推，共有10个）
=5+2*10

wubin

"<>"what it mean?

joywzy

以下是引用wubin在2003-6-2 16:30:00的发言：
"<>"what it mean?

不等于.

joywzy

谢谢祈晴坊主,第5题明白了.

那么第1题呢?谢谢.

joywzy

请教第1题的思路,谢谢.

lavender

以下是引用greenfish在2003-5-26 12:41:00的发言：
60% of incorrect paper record(P')=75% of incorrect electric record(E')=3% of all, 即0.6P'=0.75E'=0.03=P'E'，求出P'=0.05，E'=0.04，所以PE(both correct paper and correct electric record)=1-P'-E'+P'E'=0.94

0.03=P'E'???  'E'=0.02? or 0.03?