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GRE Quantitative Practice, Numeric Entry

Question 3

If Jason draws two marbles randomly from a bag containing six marbles — three red and three blue — what is the probability that he will draw two blue marbles from the bag?

Give your answer as a fraction.


Explanatory Answer

The probability that the first marble drawn will be blue is 3 in 6, or 1/2. With five marble remaining — two blue and three red — the probability of drawing another blue marble is 2 in 5, or 2/5. To determine the probability of both events occurring, combine individual probabilities by multiplication. The product of 1/2 and 2/5 is 2/10, or 1/5. The correct answer is 1/5 (or an equivalent fraction such as 2/10).