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    Question

    ‘A’ alone can complete a work in 15 days. ‘B’

    alone can complete the same work in 20 days. If ‘A’ and ‘B’ work together for 5 days, then the remaining work can be completed by ‘A’ alone in how many days?
    A 6.25 days Correct Answer Incorrect Answer
    B 6.5 days Correct Answer Incorrect Answer
    C 5.25 days Correct Answer Incorrect Answer
    D 5.5 days Correct Answer Incorrect Answer

    Solution

    Let the total amount of work = 60 units {LCM of 15 and 20} Then, efficiency of ‘A’ = 60/15 = 4 units/day Efficiency of ‘B’ = 60/20 = 3 units/day Combined efficiency of ‘A’ and ‘B’ = 4 + 3 = 7 units/day Work completed by ‘A’ and ‘B’ together in 5 days = 5 × 7 = 35 units Remaining work = 60 – 35 = 25 units Time taken by ‘A’ alone to complete the remaining work = 25/4 = 6.25 days

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