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    Question

    10 defective pens are accidentally mixed with 140

    good ones. It is not possible to just look at a pen and tell whether or not it is defective. One pen is taken out at random from this lot. Determine the probability that the pen is taken out is a good one.
    A 0.916 Correct Answer Incorrect Answer
    B 0.933 Correct Answer Incorrect Answer
    C 0.932 Correct Answer Incorrect Answer
    D 0.884 Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Numbers of pens = Numbers of defective pens + Numbers of good pens
    ∴ Total number of pens = 140 + 10 = 150 pens
    P(E) = (Number of favourable outcomes) / (Total number of outcomes)
    P(picking a good pen) = 140/150 = 14/15 = 0.933

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