Problem-Solving and Data AnalysisMediumProbability of a multiple
Problem-Solving and Data Analysis practice question
An integer from 1 to 20 is chosen at random. What is the probability that it is a multiple of 3?
- A. 3/10Correct
- B. 1/3
- C. 7/20
- D. 1/4
Answer: A. 3/10
The multiples of 3 from 1 to 20 are 3, 6, 9, 12, 15 and 18 — six of twenty numbers. 6/20 = 3/10.
Why the other answers are wrong
- B. 1/3
- 1/3 would be right for a very long run of integers, but 20 is not a multiple of 3; only 6 of the 20 qualify.
- C. 7/20
- 7/20 counts seven multiples; 21 is outside the range.
- D. 1/4
- 1/4 would be 5 multiples out of 20; there are 6.
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