There are 30 people in my math class. 12 of them have cool dads, 18 of them have cool moms, and 9 of them have cool dads and cool moms. How many people have moms and dads who are both uncool?
12 - 9 = cool dads only = 3
18 - 9 = cool moms only = 9
30 - ( 3 + 9 + 9) =
30 - 21 =
9 have both uncool
