Probability Answers

Probability - Quant/Math - CAT 2008

Question 4 the day: October 10, 2003

The question for the day is from the topic of Probability.

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

(1)	17/30			(2)	2/5
(3)	11/30			(4)	4/15

Correct Answer - (2)

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Solution:


The probability that the number is a multiple of 3 is 10/30. (Since 3*10 = 30).

Similarly the probability that the number is a multiple of 13 is 2/30. {Since 13*2 = 26).

Neither 3 nor 13 has common multiple from 1 to 30. Hence these events are mutually exclusive events. Therefore chance that the selected number is a multiple of 3 or 13 is (10+2)/30 = 2/5