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If Rahul rows 15 km upstream in 3 hours and 21 km downstream in 3 hours, then the speed of the stream is

  • 5 km/hr
  • 4 km/hr
  • 2 km/hr
  • 1 km/hr

Answer: Option D

Explanation:

Rate upstream = (15/3) kmph
Rate downstream (21/3) kmph = 7 kmph.
Speed of stream (1/2)(7 - 5)kmph = 1 kmph

Similar Questions :

1. If Rahul rows 15 km upstream in 3 hours and 21 km downstream in 3 hours, then the speed of the stream is

  • 5 km/hr
  • 4 km/hr
  • 2 km/hr
  • 1 km/hr

Answer: Option D

Explanation:

Rate upstream = (15/3) kmph
Rate downstream (21/3) kmph = 7 kmph.
Speed of stream (1/2)(7 - 5)kmph = 1 kmph

2. Sahil can row 3 km against the stream in 20 minutes and he can return in 18 minutes. What is rate of current ?

  • 1/2 km/hr
  • 1/3 km/hr
  • 2 km/hr
  • 4 km/hr

Answer: Option A

Explanation:

Speed Upstream=32060=9km/hrSpeed Downstream=31860=10km/hrRate of current will be10−92=12km/hr

3. A boat can travel with a speed of 16 km/hr in still water. If the rate of stream is 5 km/hr, then find the time taken by the boat to cover distance of 84 km downstream.

  • 4 hours
  • 5 hours
  • 6 hours
  • 7 hours

Answer: Option A

Explanation:

It is very important to check, if the boat speed given is in still water or with water or against water. Because if we neglect it we will not reach on right answer. I just mentioned here because mostly mistakes in this chapter are of this kind only.

Lets see the question now.
Speed downstream = (16 + 5) = 21 kmph

Time = distance/speed = 84/21 = 4 hours

4. A man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. The ratio of the speed of the boat in still water and stream is

  • 3:1
  • 1:3
  • 2:4
  • 4:2

Answer: Option A

Explanation:

Let speed downstream = x kmph
Then Speed upstream = 2x kmph

So ratio will be,
(2x+x)/2 : (2x-x)/2
=> 3x/2 : x/2 => 3:1

5. A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is

  • 2 km/hr
  • 3 km/hr
  • 4 km/hr
  • 5 km/hr

Answer: Option D

Explanation:

Let the speed of the stream be x km/hr. Then,
Speed downstream = (15 + x) km/hr,
Speed upstream = (15 - x) km/hr

So we know from question that it took 4(1/2)hrs to travel back to same point.

So,
3015+x−3015−x=412=>900225−x2=92=>9x2=225=>x=5km/hr

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