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A steamer goes downstream from one port to another in 4 hours, it covers the same distance upstream in 5 hours. If the speed of the stream is 2km/hr,the distance between the two parts is_______?

Correct answer: D. 80 km

  • A. 50km
  • B. 60km
  • C. 70km
  • D. 80 km

Explanation

Let the distance be D km. The downstream speed is D/4 km/hr and the upstream speed is D/5 km/hr; their difference is 2 km/hr + 2 km/hr = 4 km/hr because the stream changes the boat's speed by 2 km/hr in opposite directions. Thus D/4 - D/5 = 4 km/hr, so D/20 = 4 km and D = 80 km. The likely mistake is choosing option c, 70 km, from subtracting the travel times instead of the speeds.

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About Time, Speed and Distance

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