There are 15 slate rocks, 20 pumice rocks, and 10 granite rocks randomly distributed in a certain field. If 2 rocks are

[BTGmoderatorDC]

There are 15 slate rocks, 20 pumice rocks, and 10 granite rocks randomly distributed in a certain field. If 2 rocks are to be chosen at random and without replacement, what is the probability that both rocks will be slate rocks?

A) 1/3
B) 7/22
C) 1/9
D) 7/66
E) 2/45


OA D

Source: GMAT Prep

[Scott@TargetTestPrep]

There are 15 slate rocks, 20 pumice rocks, and 10 granite rocks randomly distributed in a certain field. If 2 rocks are to be chosen at random and without replacement, what is the probability that both rocks will be slate rocks?

A) 1/3
B) 7/22
C) 1/9
D) 7/66
E) 2/45


OA D

Solution:

The probability of getting two slate rocks is 15/45 x 14/44 = 1/3 x 7/22 = 7/66.

Answer: D