有题不会，请指教

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 Q?

A. 20          B. 24                   C.30                D.50         E.52  

正确答案是：A

Which of the following could not be the number of persons in the surveyed group who had eaten at both P and Q?”
下面哪个不可能是在P和Q都吃过饭的人数？

其实这到题就是求范围，画图，可得在两家都吃过饭的人数范围[24，52]