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      Question

      β€˜A’ alone can complete a work in 50 hours. β€˜A’

      started the work alone and left after working on it for 30 hours. If β€˜B’ completed the rest of the work in 20 hours then find the time taken by β€˜A’ and β€˜B’ together to complete the whole work.
      A 20 hours Correct Answer Incorrect Answer
      B 22 hours Correct Answer Incorrect Answer
      C 25 hours Correct Answer Incorrect Answer
      D 23 hours Correct Answer Incorrect Answer
      E None of these Correct Answer Incorrect Answer

      Solution

      Let the total work = 200 units Then, efficiency of β€˜A’ = (200/50) = 4 units/hour Work completed by β€˜A’ alone in 30 hours = 4 Γ— 30 = 120 units Remaining work = 200 – 120 = 80 units So, efficiency of β€˜B’ = 80/20 = 4 units/hour Therefore, combined efficiency of β€˜A’ and β€˜B’ = 4 + 4 = 8 units/hour So, time taken by β€˜A’ and β€˜B’ together to complete the work = (200/8) = 25 hours

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