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      Question

      ‘A’ alone can complete a work in 15 days while

      ‘A’ and ‘B’ together can complete the same work in 10 days. How much percentage of the work, ‘B’ alone can complete in 21 days?
      A 75% Correct Answer Incorrect Answer
      B 77% Correct Answer Incorrect Answer
      C 70% Correct Answer Incorrect Answer
      D 79% Correct Answer Incorrect Answer
      E 80% Correct Answer Incorrect Answer

      Solution

      Let the total work = L.C.M of 15 and 10 = 30 units Then, efficiency of ‘A’ alone = 30 ÷ 15 = 2 units/day Combined efficiency of ‘A’ and ‘B’ = 30 ÷ 10 = 3 units/day So, efficiency of ‘B’ = 3 – 2 = 1 units/day So, work done by ‘B’ alone in 21 days = 1 × 21 = 21 units So, percentage of work completed by ‘B’ = (21 ÷ 30) × 100 = 70%

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