Boats and Streams- Aptitude Questions and Answers

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A man can row upstream 32 km in 4 hours. If the speed of current is 2 km/hr, find how much he can go downstream in 6 hours ?

A)
70 km

B)
72 km

C)
64 km

D)
81 km


Correct Answer :

72 km


Explanation :

Upstream Speed(S) = Distance(d)/Time(t) = 32/4 km/hr= 8 km/hr

If The speed of boat or boatman in still water is U kmph and The speed of water or stream is V kmph, then:
Speed upstream = (U - V) kmph
8 = U - 2
Speed of man in still water,U = 8 + 2 = 10 km/hr

Speed of man in downstream = (U + V) kmph = (10 + 2) = 12 km/hr
Now, man cover the distance in 6 hours = 12 * 6 = 72 km

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If a man rows at 5 km/hr in still water and 3.5 km/hr against the current,then his rate along the current is ?

A)
8.5 km/hr

B)
6.5 km/hr

C)
6 km/hr

D)
4.25 km/hr


Correct Answer :

6.5 km/hr


Explanation :

If The speed of boat or boatman in calm water is u kmph and The speed of water or stream is v kmph, then:In water, the speed along with stream= (u + v) kmph

Speed of current = 5 - 3.5 = 1.5 km/hr.

So the speed of man along the current = 5 + 1.5 = 6.5 km/hr

The speed of a boat downstream is 15 km/hr and the speed of the stream is 1.5 km/hr. The speed of the boat upstream is ?

A)
13.5 km/hr

B)
16.5 km/hr

C)
12 km/hr

D)
8.25 km/hr


Correct Answer :

12 km/hr


Explanation :

If The speed of boat or boatman in calm water is u kmph and The speed of water or stream is v kmph, then:
Speed downstream= (u + v) kmph , In water, the speed along with stream
Speed upstream = (u - v) kmph ,In water, the speed against the stream

15= u + 1.5
⇒ u = 13.5

Speed upstream, u - v = (13.5 - 1.5) km/hr = 12 km/hr

A boat goes 14 km upstream in 56 minutes. The speed of stream is 2 km/hr. The speed of boat in still water is ?

A)
6 km/hr

B)
15 km/hr

C)
14 km/hr

D)
17 km/hr


Correct Answer :

17 km/hr


Explanation :

Speed upstream Speed(S) = Distance(d)/Time(t) = 14/56 km/min = 14*60/56 km/hr= 15 km/hr

If The speed of boat or boatman in still water is U kmph and The speed of water or stream is V kmph, then:
Speed upstream = (U - V) kmph ,In water, the speed against the stream
15 = U - 2
So speed of boat in still water , U = 17 km/hr

A man can row upstream at 15 km/h and downstream at 21 km/h. The speed of water current of the river is ?

A)
8 km/h

B)
6 km/h

C)
3 km/h

D)
5 km/h


Correct Answer :

3 km/h


Explanation :

If the speed downstream is x kmph and the speed upstream is y kmph, then:
Rate of stream = 1/2 (x - y) kmph.

= 1/2(21 - 15) km/h
= 3 km/h

A man rows downstream 60 km and upstream 36 km, taking 4 hours each time. The speed of the man is :

A)
15 km/h

B)
16 km/h

C)
8 km/h

D)
12 km/h


Correct Answer :

12 km/h


Explanation :

If the speed downstream is x kmph and the speed upstream is y kmph, then:
Speed in still water = 1/2 (x + y) kmph.

x = 60/4 =15 km/h
y = 36/4 = 9 km/h
speed of the man = (15 + 9) / 2 = 12 km/h

The speed of a boat in still water is 15 km/hr and the rate of current is 3 km/hr. The distance travelled downstream in 12 minutes is?

A)
1.2 km

B)
1.8 km

C)
2.4 km

D)
3.6 km


Correct Answer :

3.6 km


Explanation :

Speed Downstream = (15 + 3) km/hr = 18 km/hr.

Distance travelled =(18 * 12 / 60 )hrs = 3.6 km

The speed of a boat in downstream is 12 km / h and in upstream is 8 km / h. The time taken by boat to cover 24 km in still water?

A)
2 hours

B)
3 hours

C)
2.4 hours

D)
1.2 hours


Correct Answer :

2 hours


Explanation :

If The speed of boat or boatman in still water is U kmph and The speed of water or stream is V kmph, then:
Speed upstream = (U - V) = 8 km/hr
Speed of man in downstream = (U + V) kmph = 12 km/hr

After solving above equations 2*U = 20 km/hr
speed of boat in still water is,U = 10 km/hr

Required time = 24 / 10 = 2.4 hr

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