我举个例子，
Of the 800 students at a certain college, 250 students live on campus and are more than 20 yearsold.How many of the 800 students live on campus and are 20 years old or less?
(1)640 students at the college are more than 20 years old.
(2)60 students at the college are 20 years old or less and live off campus.
Prep给出的思路是列表(如下)
campus ~ campus
>20250b
小于等于20 c d
Total:800
这个思路可以应用到这一类题型上，而据我观察，8月份和11月份的两次机经中都多次出现这种题目，如果在prep中做过类似的题目，考场上就能举一反三啦。
