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      Question

      β€˜A’ alone can complete a work in 40 hours. β€˜A’

      started the work alone and left after working on it for 20 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 32 hours Correct Answer Incorrect Answer
      B 20 hours Correct Answer Incorrect Answer
      C 30 hours Correct Answer Incorrect Answer
      D 25 hours Correct Answer Incorrect Answer
      E None of these Correct Answer Incorrect Answer

      Solution

      Let the total work = 360 units Then, efficiency of β€˜A’ = (360/40) = 9 units/hour Work completed by β€˜A’ alone in 20 hours = 9 Γ— 20 = 180 units Remaining work = 360 – 180 = 180 units So, efficiency of β€˜B’ = 180/20 = 9 units/hour Therefore, combined efficiency of β€˜A’ and β€˜B’ = 9 + 9 = 18 units/hour So, time taken by β€˜A’ and β€˜B’ together to complete the work = (360/18) = 20 hours

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