Question

Twenty-one students at a school have an allergy to peanuts, shellfish, or both.

 Fourteen students at the school are allergic to peanuts.
 Twelve students at the school are allergic to shellfish.
How many of the students are allergic to both peanuts and shellfish?
A 12
B 7
C 5
D 2

Answer 1

add the 14 and the 12. You get 26, then subtract it by the total number of students, 21, then you get 5.