At Daifu university, 40% of all students are both members of a student organization and want to reduce their tuition costs. 20% of those students who want to reduce tuition are not members of the student organization. What percentage of all Daifu students want to reduce tuition?


* 20%
* 30%
* 40%
* 50%
* 60%

please give the source of this problem. if you don't give the source within the next few days, then unfortunately, we'll have to delete the problem.

thanks

The source is above

use a double set matrix. the key is the realization that the 40% is an absolute percentage, but the 20% is a percentage OF a different quantity in the problem (read it carefully!). you can set the total to 100, because there's no indication of the total number of students.