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    Question

    ‘A’ alone can complete a work in 20 days. ‘B’

    alone can complete the same work in 25 days. If ‘A’ and ‘B’ work together for 7 days, then the remaining work can be completed by ‘A’ alone in how many days?
    A 5.4 days Correct Answer Incorrect Answer
    B 6.4 days Correct Answer Incorrect Answer
    C 7.4 days Correct Answer Incorrect Answer
    D 8.4 days Correct Answer Incorrect Answer

    Solution

    Let the total amount of work = 100 units {LCM of 20 and 25} Then, efficiency of ‘A’ = 100/20 = 5 units/day Efficiency of ‘B’ = 100/25 = 4 units/day Combined efficiency of ‘A’ and ‘B’ = 5 + 4 = 9 units/day Work completed by ‘A’ and ‘B’ together in 7 days = 7 × 9 = 63 units Remaining work = 100 – 63 = 37 units Time taken by ‘A’ alone to complete the remaining work = 37/5 = 7.4 days

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