求助：狒狒 宝典上的一道数学题

zhufeisophie

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?
            

答案：设总数为X policies，则既有非P又有非E为3%X；60%的非P中为非E，则非P为3%X/60%；75%的非E为非P，则非E为3%/75%，那么非P与非E一共有（3%X/60%+3%X/75%-3%X）
                ，那么P与E一共有X-（3%X/60%+3%X/75%-3%X），则其概率为[X-（3%X/60%+3%X/75%-3%X）]/X=94%

最后的问题的意思是求 既有 correct paper record，也有 correct electric record 的记录的概率，还是求或者 有 correct paper record，或者有 correct electric record 的记录的概率？ 个人感觉求的是既有 correct paper record，也有 correct electric record 的记录的概率，但看答案，求出的好像是或者 有 correct paper record，或者有 correct electric record 的记录的概率。请大家指点！多谢啦~~

mymengming

这题好像没有答案的。如图

如图，I/IP=60%

I/IE=75%

I/P+E-T=3%

求的是(T-I)/(P+E-T)

由于T/(P+E-T)为未知数，所以不可求出，请检查是否抄错了题目

谢谢