Q15

If R=P/Q, is R=P?

(1)P>50

(2)0<Q=20

这题答案是E,可是我觉得（2）既然已有Q=20的条件，那么R肯定不等于P啊...还是题目错了，是0<Q<20??谢谢...

Q35

For what percent of those tested for a certain infection was the test accurate; that is, positive for those who had the infection and negative for those who did not have the infection?

(1)Of those who tested positive for the infection, 1/8 did not have the infection.

(2)Of those tested for the infection, 90 percent tested negative.

这题没看懂题目...可以请大虾解释下不？嘿嘿...是问测试的准确率不？没有准确率的定义啊...是否(1)(2)合起来，还缺少一个what percent of those who are tested negtive but actually have the infection??

写到这里突然想起来，15题难道还要考虑P=R=0的情况？所以，即使Q=20也不能说PR不相等？谢谢谢谢...

15题,我估计是<=,那么还是E.

35

设检验为阴性的人有x%是已经被感染的，即漏查率为x%

设做了n次检验

则正确的为：10%n{呈阳性的}*（7/8）{阳性准确率}+90%n{呈阳性的}*(x%){阳性准确率}

加起来就成为N次试验里面正确的次数

比上总次数n就是这种检验的准确率了

整理得

0.1*(7/8)+0.9*X%

X未知，所以求不出来。