# If 75 percent of a class answered the first question…

## Solution:

For this overlapping sets problem we can use the following equation:

Total percent = % in category A + % in category B – % in both categories + % in neither categories

Since the answer choices are in percentage form we can use 100 as the total. We are given that 75 percent of a class answered the first question on a certain test correctly, 55 percent answered the second question on the test correctly, and 20 percent answered neither of the questions correctly. Using these values, we have:

100 = 75 + 55 – B + 20

100 = 150 – B

B = 50