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    Question

    A can do a work in 20 days, B can do in 30 days and C

    can do in 60 days. If A is helped by B and C every third day. The number of days they will take to competed the work is:
    A 15 days Correct Answer Incorrect Answer
    B 18 days Correct Answer Incorrect Answer
    C 12 days Correct Answer Incorrect Answer
    D 9 days Correct Answer Incorrect Answer

    Solution

    ATQ, The efficiency of A is 1/20 The efficiency of B is 1/30 The efficiency of C is 1/60 1st day work by A = 1/20 2nd day work by A = 1/20 3rd day work by A + B + C = 1/20 + 1/30 + 1/60 ⇒ (3 + 2 + 1)/60 = 1/10 Work completed in 3 days ⇒ 1/20 +1/20 + 1/10 = 1/5 Time is taken to complete the work ⇒ 3 × 5 = (1/5) × 5 ⇒ 15 days = 1 ∴ In 15 days the work will be completed.

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