Wednesday 27 November 2013

Question on Probability

Out of all the 2-digit integers between 1 and 100, a 2-digit number has to be selected at random. What is the probability that the selected number is not divisible by 7?

(A) 13/90
(B) 12/90
(C) 78/90
(D) 77/90

Answer : (D)

Explanation:
Number of 2 digit numbers between 1 and 100 = 90

2 digit numbers between (10 and 99) that are divisible by 7 : 7, 14, 21, 28, 35, 42, 49, 56, 73, 70, 77, 84, 91, 98

Number of 2 digit numbers between (10 and 99) that are divisible by 7 = 13.

Number of 2 digit numbers between (10 and 99) that are NOT divisible by 7 = 90 - 13 = 77

So, the probability that a number is NOT divisible by 7 = 77/90

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