Boats & Streams

Ladakh Prison Department · Mathematics · 20 practice questions with answers and explanations: 4 Easy, 16 Medium, 0 Hard.

Sample questions

Sample Easy question 1

A man rowing upstream against a 5 km/h stream moves at 10 km/h. What is his speed in still water?

  1. 5
  2. 20
  3. 15
  4. 10
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Answer: C. Upstream speed = x − 5 = 10, so x = 15 km/h.

Sample Easy question 2

A boat's speed in still water is 8 km/h and the stream flows at 2 km/h. How long will it take to travel 36 km upstream?

  1. 5 hours
  2. 4.5 hours
  3. 7.2 hours
  4. 6 hours
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Answer: D. Upstream speed = 8 − 2 = 6 km/h. Time = 36 ÷ 6 = 6 hours.

Sample Easy question 3

A boat's speed in still water is 15 km/h and the stream flows at 3 km/h. Find its speed downstream.

  1. 45
  2. 15
  3. 18
  4. 12
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Answer: C. Downstream speed = boat + stream = 15 + 3 = 18 km/h.

Sample Medium question 4

A boat covers 20 km downstream in 2 hours and the same distance upstream in 5 hours. Find the speed of the boat in still water.

  1. 8
  2. 10
  3. 6
  4. 7
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Answer: D. Downstream = 10 km/h, upstream = 4 km/h. Still water = (10 + 4) ÷ 2 = 7 km/h.

Sample Medium question 5

The speed of a boat in still water is 5 times the speed of the stream. What is the ratio of the time taken to cover a given distance downstream to the time taken upstream?

  1. 1 : 5
  2. 3 : 2
  3. 2 : 3
  4. 5 : 6
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Answer: C. Let the stream be s: downstream 6s, upstream 4s. For equal distance, time is inversely proportional to speed, so the ratio is 4 : 6 = 2 : 3.

Sample Medium question 6

A boat goes 30 km downstream and returns the same distance upstream. If the speed of the boat in still water is 15 km/h and the speed of the stream is 5 km/h, find the total time taken for the round trip.

  1. 4 1/2 hours
  2. 5 1/2 hours
  3. 3 hours
  4. 4 hours
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Answer: A. Downstream speed = 20 km/h, upstream speed = 10 km/h. Time = 30/20 + 30/10 = 4 1/2 hours.

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