Answer:
c. 18
Step-by-step explanation:
Given that the contraceptive has an effectiveness of 82%, I am assuming this implies that 82% of 100 or 82 couples will not get pregnant which leaves 18 couples left who will. This math simply involves subtraction of the total couples from the total couples multiplied by the percent effectiveness: total # couples - % effectiveness × total # couples.
100 - 82% of 100 = 100 - 82 = 18