Problems on Boats and Streams

Problems on Boats and Streams

Learn and practice Problems on boats and streams with easy explaination and shortcut tricks. All questions and answers on number covered for various Competitive Exams

Solve Problems:

1) The speed of a boat in still water is 5km/hr. If the speed of the boat against the stream is 3 km/hr, what is the speed of the stream?

  1. 1.5 km/hr
  2. 2 km/hr
  3. 2.5 km/hr
  4. 1 km/hr
View Answer

The correct answer is B

Answer with explanation:

Let the speed of stream = X km/hr

Speed of boat = 5 km/hr

Speed upstream = 3km/hr

Apply formula: Speed upstream = speed of boat – speed of stream

∴ 3 = 5 – X

X = 5 – 3 = 2 km/hr

2) A man rows downstream at 20 km/hr and rows upstream at 15 km/hr. At what speed he can row in still water?

  1. 17.5 km/hr
  2. 18 km/hr
  3. 20.5 km/hr
  4. 22 km/hr
View Answer

The correct answer is A

Apply formula: Speed in still water = (speed downstream + speed upstream)

Speed downstream = 20 km/hr

Speed upstream = 15 km/hr

∴ Required speed =  (20 + 15) km/hr

=  ∗ 35 = 17.5 km/hr

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3) A man swims 12 km downstream and 10 km upstream. If he takes 2 hours each time, what is the speed of the stream?

  1. 1 km/hr
  2. 0.5 km/hr
  3. 1.5 km/hr
  4. 0.7 km/hr
View Answer

The correct answer is B

Answer with explanation:

Speed downstream =  Distance/Time= 12/2 = 6 km/hr

Speed downstream = Distance/Time = 10/2 = 5 km/hr

Apply formula: Speed of stream =  (speed downstream – speed upstream)

X = 6 km/hr

Y= 5 km/hr

∴ Required speed =  (6 -5) km/hr

=  ∗ 1= 0.5 km/hr

4) A boat covers 800 meters in 600 seconds against the stream and returns downstream in 5 minutes. What is the speed of the boat in still water?

  1. 1 m/s
  2. 1.5 m/s
  3. 2 m/s
  4. 2.5 m/s
View Answer

The correct answer is C

Answer with explanation:

Speed upstream = Distance/Time = 800/600 = 8/6 m/s

Speed downstream = Distance/Time = 800/(5*60) = 8/3 m/s

Apply formula: Speed in still water =  (speed downstream + speed upstream)

X = 8/3 m/s

Y = 8/6 m/s

∴ Speed in still water = (8/3 + 8/6)

=  ∗ 4 = 2 m/s

5) A man can row a boat at a speed of 20 km/hr in still water. If the speed of the stream is 5 km/hr, in what time he can row a distance of 75 km downstream?

  1. 1.5 hours
  2. 2 hours
  3. 2.5 hours
  4. 3 hours
View Answer

The correct answer is D

Answer with explanation:

Speed of boat = 20 km/hr

Speed of stream = 5 km/hr

∴ Speed downstream = 20 + 5= 25 km/hr

Required Time = Distance/Time = 75/25 = 3 hours

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6) A man swimming in a river which is flowing at 3 km/hr finds that in a given time he can swim twice as far downstream as he can swim upstream. What will be his speed in still water?

  1. 9.5 km/hr
  2. 10 lm/hr
  3. 10.5 km/hr
  4. 11 km/hr
View Answer

The correct answer is C

Answer with explanation:

Let the man swims at X km/hr in still water.

As per the question, he covers twice the distance downstream as he covers upstream in a given time.

Distance = Speed ∗ Time

∴ Speed downstream ∗ Time = 2 (Speed upstream ∗ Time)

Time is same in both the cases.

∴ X+3 =2∗ (X – 3 Apti Boat and streams 36 )

X + 7/2 = 2∗ (X -7/2)

X + 7/2 =2X – 7

X-2X = -7 – 7/2

X = 21/2 = 10.5 km/hr

7) A man can row at 12 km/hr in still water. He finds that he takes twice as much time to row upstream than to row downstream when he covers a certain distance. Find the speed of the stream.

  1. 4 km/hr
  2. 3 km/hr
  3. 4.5 km/hr
  4. 3.5 km/hr
View Answer

The correct answer is A

Answer with the explanation:

As per the question, he takes twice the time when he rows upstream than rowing downstream.

Time is inversely proportioned to speed. So he rows at twice the speed when moving along the stream than moving against the stream.

Let his speed upstream = X km/hr

And, his speed downstream = 2X

∴ Speed in still water = 1/2 (2X+X) = 1.5 X km/hr

As per the question;

1.5X = 12 km/hr

X = 120/15 =8 km/hr

Speed upstream = 8 km/hr

So, speed downstream = 2 ∗ 8= 16 km/hr

Speed of current = (speed downstream – speed upstream)

=  (16 – 8)

=  * 8 = 4 km/hr

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8) A boat takes 6 hours to move downstream from point P to Q and to return to point P moving upstream. If the speed of the stream is 4 km/hr and speed of the boat in still water is 6 km/hr, what is the distance between point P and Q?

  1. 8 km
  2. 9 km
  3. 10 km
  4. 11 km
View Answer

The correct answer is C

Answer with the explanation:

Let the distance between points P and Q = X km

Speed downstream = 6 + 4= 10 km/hr

Speed upstream = 6 – 4 = 2 km/hr

Time = Distance/Time

So, as per question;

x/10 + x/2 = 6 hours

(x+5x)/10 = 6

6X = 60

X = 10 km

9) A man can swim in still water at 8 km/hr. If the river is flowing at 2km/hr he takes 80 minutes to reach a place and return back, how far is the place?

  1. 4 km
  2. 3 km
  3. 4.5 km
  4. 5 km
View Answer

The correct answer is D

Answer with the explanation:

Let the place is X km far.

Speed downstream = 8+2=10 km/hr

Speed upstream = 8 – 2 = 6 km/hr

Time = Distance/Time

So, as per question;

x/6 + x/10 = 80/60

(10x+6x)/60 = 4/3

30X + 18X = 240

48X = 240

X = 240/48 = 5 km

10) A motorboat travels 16 km in 2 hours against the flow of river and travels next 8 km along the flow of the river in 20 minutes. How long will it take motorboat to travel 48 km in still water?

  1. 2.5 hours
  2. 3 hours
  3. 3.5 hours
  4. 4 hours
View Answer

The correct answer is B

Answer with the explanation:

Speed = Distance/Time

Speed upstream = 16/2 = 8 km/hr

Speed downstream =  8/ (20/60)= 480/20 = 24 km/hr

∴ Speed in still water =  (speed downstream +speed upstream)

=  (24+8)=16 km/hr

Required time = Distance/Speed in steel ater

= 48/16 =3 hour

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