Boats & Streams

LSSSSB Non-Technical · Mathematics · 20 practice questions with answers and explanations: 4 Easy, 16 Medium, 0 Hard.

Sample questions

Sample Easy question 1

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 2

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 Easy question 3

A boat's speed in still water is 12 km/h and the stream flows at 4 km/h. Find its speed upstream.

  1. 8
  2. 3
  3. 16
  4. 12
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Answer: A. Upstream speed = boat − stream = 12 − 4 = 8 km/h.

Sample Medium question 4

A man rows at 6 km/h in still water and the river flows at 2 km/h. How long does he take to row 16 km downstream and come back?

  1. 8 hours
  2. 4 hours
  3. 5 hours
  4. 6 hours
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Answer: D. Downstream 8 km/h: 16 ÷ 8 = 2 h. Upstream 4 km/h: 16 ÷ 4 = 4 h. Total 6 hours.

Sample Medium question 5

A boat takes 3 hours to go 36 km downstream and 4 hours to come back 36 km upstream. Find the speed of the boat in still water.

  1. 9
  2. 10
  3. 12
  4. 10.5
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Answer: D. Downstream = 12 km/h, upstream = 9 km/h. Still water = (12 + 9) ÷ 2 = 10.5 km/h.

Sample Medium question 6

A man rows 24 km upstream and 24 km back downstream in 5 hours. If the stream flows at 2 km/h, find his speed in still water.

  1. 14
  2. 8
  3. 10
  4. 12
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Answer: C. 24/(x − 2) + 24/(x + 2) = 5 → 48x = 5(x² − 4) → 5x² − 48x − 20 = 0 → x = 10. Check: 24/8 + 24/12 = 3 + 2 = 5.

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