[求助]请教prep DS1-10

lilyblue_zl

10. 

Of the 800 students at a certain college, 250 students live on campus and are more than 20 years old.  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.

答案选C

我画出集合图反而没有思路了。求解。

顺便问一下，prep math中显示绿色的题目是什么意思啊？

lilyblue_zl

是破解的prep里面的

alanis_liu

lZmm,请问你做的这个prep是破解版本吗？还是08年新的prep software里的啊？ 這題由1条件只能推出 390 more than 20 的同学 off-campus。 而2条件也是没办法得出什么结论的。所以1＋2可以推出 390 more than 20 off campus, 60 less than 20 off campus, 300 less than 20 on campus, and 已知～