New Enroll in RBI Grade B New Batch - Starts on May 21

    Question

    A basket contains 3 blue, 5black and 3 red pens.

    If 3 pens are drawn at random what is the probability

    that all are black?
    A 2/33 Correct Answer Incorrect Answer
    B 1/11 Correct Answer Incorrect Answer
    C 3/11 Correct Answer Incorrect Answer
    D 8/33 Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let S be the sample space. Then, N(S) = number of ways of drawing 3 pens out of 11 = ¹¹C₃ = (11 ×10 ×9)/(3 ×2 ×1) = 165 Let E = event of getting 3 from 5 black pens. n(E) = ⁵C₃ = (5 × 4 )/(2 ×1) = 10 n(P) = (n(E))/(n(S)) = 10/165 = 2/33

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