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    Question

    Rahul used to complete 25 problems in 50 minutes. But now,

    his efficiency has dropped by 20%. How much time will he need to complete the same number of problems?
    A 62.5 mins Correct Answer Incorrect Answer
    B 116 mins Correct Answer Incorrect Answer
    C 55.5 mins Correct Answer Incorrect Answer
    D 120 mins Correct Answer Incorrect Answer

    Solution

    ATQ,

    50 minutes

    Initial efficiency of Rahul = 50 Ă· 25 = 2 minutes/question

    New efficiency = 50 Ă· (25 Ă— 0.8) = 2.5 minutes/question

    So, time required to finish 25 questions = 2.5 Ă— 25 = 62.5 minutes

    Alternate Solution:

    Ratio of new efficiency to old = 0.8:1 = 4:5

    So, ratio of new time to old = 5:4

    Required time taken = 50 Ă— (5/4) = 62.5 minutes

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