Question

In a group of 36 students, 6 study both Art and Biology.

13 study Biology but not Art.
2 study neither subject.
How many study Art?

Answer 1

21

Explanation:

this is really easy so what you do is

you know 13 study bio and NOT art

we also know 2 student study neither subject

so lets just do 36-15

which is 21, this 21 does include the 6 that study both and the rest we can safely assume study art

Answer 2

17

Explanation:

because 19 students for the other in total (you add the ones who study biology and the ones who study both, then you minus the group of students by 19)