In a group of 68 students, each student is registered for at least one of three classes – History, Math and English. Twenty-five students are registered for History, twenty-five students are registered for Math, and thirty-four students are registered for English. If only three students are registered for all three classes, how many students are registered for exactly two classes?
13
10
9
8
7
Please explain this for me. But actually, I am curious why the formula does not work here with this question.
n(a+b+c) = n(a)+n(b)+n(c)-{n(a+b)+n(b+c)+n(a+c)}-n(a+b+c)
The ansewr is 10
13
10
9
8
7
Please explain this for me. But actually, I am curious why the formula does not work here with this question.
n(a+b+c) = n(a)+n(b)+n(c)-{n(a+b)+n(b+c)+n(a+c)}-n(a+b+c)
The ansewr is 10
