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A number is selected at random from the first 30 natural

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by Jay@ManhattanReview » Mon Nov 04, 2019 11:07 pm
BTGmoderatorLU wrote:Source: Economist GMAT

A number is selected at random from the first 30 natural numbers. What is the probability that the number is a multiple of either 3 or 13?

A. 17/30
B. 2/5
C. 7/15
D. 4/15
E. 11/30

The OA is B
From 1 to 30, there are 10 multiples of 3: (3, 6, 9, ..., 30), and there are 2 multiples of 13: (13, 26). So, there are a total of 10 + 2 = 12 multiples of 3 or 13.

Thus, the probability that the number is a multiple of either 3 or 13 = 12/30 = 2/5

The correct answer: B

Hope this helps!

-Jay
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