A commuter survey counts the people riding in cars on a highway in the morning. Each car contains only one man, only one woman, or both one man and one woman. Out of 25 cars, 13 contain a woman and 20 contain a man. How many contain both a man and a woman?
The correct answer is 8. The total 20 + 13 = 33, but only 25 cars have been scored. Therefore, 33 – 25, or 8 cars must have had both a man and a woman inside.