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

    Question

    A box consists of 125 apples out of which 25 are rotten.

    Khushboo comes to buy non-rotten apple. The shopkeeper takes out two apples and hands it over to Khushboo one after another. If the apple is not rotten she buys else the shopkeeper keeps them back. What is the probability that Khushboo buys at least one apple?
    A 124/155 Correct Answer Incorrect Answer
    B 23/25 Correct Answer Incorrect Answer
    C 24/25 Correct Answer Incorrect Answer
    D 495/155 Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Case I: Khushboo buys two apples
    Probability of buying first apple = (125 - 25)/125 = 100/125 = 4/5
    Probability of buying second apple = (100 - 1)/(125 - 1) = 99/124
    ∴ Probability of buying two apples = (4/5) X (99/124) = 99/155
    Case II: Khushboo buys one apple
    Probability that she is offered non-rotten apple in first attempt and rotten in second = 100/125 X 25/124 = 5/31
    Probability that she is offered rotten apple in first attempt and non - rotten in second = 25/125 X 100/125 = 4/25
    ∴ Required Probability = 99/155 + 5/31 + 4/25 = 24/25

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