A = {2, 3, 4, 5} B = {4, 5, 6, 7, 8} Two integers will be randomly selected from the sets above, one integer from set A

[BTGmoderatorDC]

A = {2, 3, 4, 5}
B = {4, 5, 6, 7, 8}

Two integers will be randomly selected from the sets above, one integer from set A and one integer from set B. What is the probability that the sum of the two integers will equal 9?


(A) 0.15
(B) 0.20
(C) 0.25
(D) 0.30
(E) 0.33


OA B

Source: Official Guide

[Brent@GMATPrepNow]

A = {2, 3, 4, 5}
B = {4, 5, 6, 7, 8}

Two integers will be randomly selected from the sets above, one integer from set A and one integer from set B. What is the probability that the sum of the two integers will equal 9?


(A) 0.15
(B) 0.20
(C) 0.25
(D) 0.30
(E) 0.33


OA B

Source: Official Guide

Here's a quick solution.

Key property: Notice that, for every number in set A, there is ONE number in set B that will produce a sum of 9.

So, if you randomly select a number from set A (), you can see that, among the 5 numbers in set B, only 1 of them will combine with your number from set A to create a sum of 9.

So, the probability of getting a sum of 9 = 1/5 = 0.2

Answer: B

Cheers,
Brent