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A box contains 3 blue marbles, 4 red, 6 green marbles and 2 yellow marbles. If two marbles are picked at random, what is the probability that they are either blue or yellow?

Correct answer: C. 2/21

  • A. 3/22
  • B. 4/21
  • C. 2/21
  • D. 1/14

Explanation

There are 3 blue plus 2 yellow marbles, so 5 favorable marbles. The probability that both selected marbles come from these five is C(5,2)/C(15,2) = 10/105 = 2/21. Students may choose 3/22 by using an incorrect total or by counting only blue marbles.

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