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      Question

      A boat travels from dock β€˜M’ to dock β€˜N’ at a

      constant speed. If its speed was increased by 8 km/h, it would have taken 4 hours less to cover the distance. It would have taken further 1 hour less if the speed was further increased by 8 km/h. The distance between dock β€˜M’ and dock β€˜N’ is:
      A 18 km Correct Answer Incorrect Answer
      B 20 km Correct Answer Incorrect Answer
      C 10 km Correct Answer Incorrect Answer
      D 50 km Correct Answer Incorrect Answer
      E None of these Correct Answer Incorrect Answer

      Solution

      According to the question, Let the original speed of the boat be β€˜x’ km/h and the original time taken to reach the destination be β€˜t’ hours. So, the distance between dock β€˜M’ and β€˜N’ = x Γ— t = xt km So, xt/(x + 8) = t – 4..........................(1) And, xt/(x + 16) = t – 4 – 1 Or, xt/(x + 16) = t – 5........................(2) Dividing equation (1) by equation (2), we get (x + 16)/(x + 8) = (t – 4)/(t – 5) So, xt – 48 – 8x + 16t = xt + 8t – x – 40 Or, 8t – 8x = 8 Or, x = t – 1 Putting the value of β€˜x’ in equation (1), we get 8tΒ² – 32t = 8tΒ² – 40t + 40 Or, t = 5 So, x = 5 – 1 = 4 Desired distance = 5 Γ— 4 = 20 km

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