Boats & Streams

JKSSB Sub-Inspector (Telecommunication) · Basic Numeracy · 12 practice questions with answers and explanations: 3 Easy, 5 Medium, 4 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 Medium question 2

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 Hard question 3

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.

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