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      Question

      A fence is constructed using 900 wooden planks. β€˜X’

      alone can place 10 planks per minute, while β€˜Y’ alone can complete the fence in 100 minutes. β€˜Z’, a curious kid, removes 4 planks per minute. If all three work together, how long will it take to finish the fence?
      A 1 hrs Correct Answer Incorrect Answer
      B 2 hrs Correct Answer Incorrect Answer
      C 5 hrs Correct Answer Incorrect Answer
      D 8 hrs Correct Answer Incorrect Answer
      E None of these Correct Answer Incorrect Answer

      Solution

      ATQ,

      Efficiency of β€˜Y’ = (900 / 100) = 9 planks/minute So, combined efficiency of β€˜X’, β€˜Y’ and β€˜Z’ = 10 + 9 – 4 = 15 planks per minute So, time taken to build the fence = (900 / 15) = 60 minutes = 1 hour

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