Multiple choice

An urn contains 3 yellow, 2 green and 2 blue playing marbles. Two marbles are drawn at random. What is the probability that none of the marbles drawn is blue?

  1. 3/7

  2. 5/7

  3. 4/21

  4. 5/21

  5. 10/21
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Total number of marbles = (3 + 2 + 2) = 7 Let S be the sample space. Then, n(S) = Number of ways of drawing 2 marbles out of 7 = 7C2 = (7 x 6)/(2 x 1) = 21 Let E be the event of drawing 2 marbles, none of which is blue (i.e. either yellow or green marble is drawn).

Therefore, n(E) = Number of ways of drawing 2 marbles out of (2 green + 3 yellow) marbles = 5C2 = (5 x 4)/(2 x 1) = 10 P(E) = n(E)/n(S) = 10/21

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