The circle graph above shows the percent of 4th graders at an elementary school who have the indicated numbers of pets in their homes. If 68 of the 4th graders have at least one pet, how many have exactly two pets?

(A) 16
(B)17
(C)20
(D)33
(E)34

“At least one” means one, two, or more than two—anything but zero pets. So that’s 30 + 20 + 35  = 85 percent of the students.

If 68 students represent 85 percent of the class, how many students represent 20%? We can do a ratio: