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      Question

      The speed of a motorboat in still water is 25 km/h and

      the speed of the stream is 5 km/h. The boat first goes 120 km downstream and then covers a certain distance upstream which is x% less than the distance travelled downstream. If the total time taken for the whole journey is 7 hours, then find ‘x’.
      A 35 Correct Answer Incorrect Answer
      B 20 Correct Answer Incorrect Answer
      C 40 Correct Answer Incorrect Answer
      D 28 Correct Answer Incorrect Answer
      E None of these Correct Answer Incorrect Answer

      Solution

      ATQ, Distance covered by boat in upstream = [{1 − (x/100)} × 120] km Upstream speed of the boat = 25 − 5 = 20 km/h Downstream speed of the boat = 25 + 5 = 30 km/h According to the question; [{{1 − (x/100)} × 120} / 20] + (120 / 30) = 7 Or, {1 − (x/100)} × (120/20) = 7 − 4 Or, {1 − (x/100)} × 6 = 3 Or, 1 − (x/100) = 3/6 Or, 1 − (x/100) = 1/2 Or, (x/100) = 1 − 1/2 = 1/2 Or, x = 50

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