Common Core: S-ID.5
Problem 17 of 25sta-017
Of 40 ninth graders, 18 play a sport. Of 60 tenth graders, 30 play a sport. A student who plays a sport is chosen at random. What is the probability that the student is a ninth grader?
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Solution walkthrough1:34
- Put the facts in a two-way table: a row for each grade, a column for sport or no sport.
- Fill in the rest. Sport column total: . All students: .
- The student is chosen from those who play a sport, so only the Sport column counts: students.
- Of those , the ninth graders number . Probability: .
- Traps: is , is , and is . Each uses the wrong total.