GRE Sample Test 1 Quantitative Reasoning 1

Question : 18 of 20

Marks: +1, -0

If the probability of selecting, without replacement, 2 red marbles from a bag containing only red and blue marbles is

3/{55}

and there are 3 red marbles in the bag, what is the total number of marbles in the bag?

Solution:

Plug In the Answers, starting with (C). If the total is 55, then the probability would be

(3/{55})(2/{54})

, which does not equal

3/{55}

. The denominator is too large, so try (B). If the total is 11, then the probability is

(3/{11})(2/{10})

, which reduces to

3/{55}

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