At North High School, a survey asked two questions, Question A and Question B. For each question, students could answer either “yes” or “no.” Of the 800 students who responded to the survey, 720 answered “yes” to Question A, and 640 answered “yes” to Question B. What is the least possible number of these students who could have answered “yes” to both questions?
- A80
- B160
- C560
- D640
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Correct answer: C
None of the 80 students ( 800 − 720) who answered “no” to Question A ( 800 − 720) could have answered “yes” to both questions.
Therefore, the least possible number of students who could have answered “yes” to both questions, can be found by subtracting the 80 who answered “no” to Question A from the 640 who answered “yes” to Question B or 640 − 80 = 560.