GRE数学题(详见补充)A survey of 100 persons revealed that 72 of them had eaten at restaurant P and that 52 of them had eaten at restaurant Q.Which of the following could not be the number of persons in the surveyed group who had eaten at bo

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GRE数学题(详见补充)A survey of 100 persons revealed that 72 of them had eaten at restaurant P and that 52 of them had eaten at restaurant Q.Which of the following could not be the number of persons in the surveyed group who had eaten at bo

GRE数学题(详见补充)A survey of 100 persons revealed that 72 of them had eaten at restaurant P and that 52 of them had eaten at restaurant Q.Which of the following could not be the number of persons in the surveyed group who had eaten at bo
GRE数学题(详见补充)
A survey of 100 persons revealed that 72 of them had eaten at restaurant P and that 52 of them had eaten at restaurant Q.Which of the following could not be the number of persons in the surveyed group who had eaten at both P and
A.20 B.24 C.30 D.50 E.52

GRE数学题(详见补充)A survey of 100 persons revealed that 72 of them had eaten at restaurant P and that 52 of them had eaten at restaurant Q.Which of the following could not be the number of persons in the surveyed group who had eaten at bo
72人有去过P
52人有去过Q
设X是P+Q都去过的人数
(72-X)是只去过P
(52-X)是只去过Q
列出不等式:(总人数须少於或等於100),另外X须少於等於52
X+72-X+52-X

如果时间充足,还可以慢慢推算。
A.20个人在P,Q都吃过,那么52个人只在P吃过,32个人只在Q吃过,这样20+52+32=104,但是调查的人只有100个,就不符了。
B.24个人在P,Q都吃过,那么48个人只在P吃过,28个人只在Q吃过,这样24+48+28=100,刚好在调查的数字范围内。
后面的一次类推。
所以A是不可能的。...

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如果时间充足,还可以慢慢推算。
A.20个人在P,Q都吃过,那么52个人只在P吃过,32个人只在Q吃过,这样20+52+32=104,但是调查的人只有100个,就不符了。
B.24个人在P,Q都吃过,那么48个人只在P吃过,28个人只在Q吃过,这样24+48+28=100,刚好在调查的数字范围内。
后面的一次类推。
所以A是不可能的。

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