Boats and Streams- Aptitude Questions and Answers

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A man can row 7.5 kmph in still water. if in a river running at 1.5 km an hour, if takes him 50 min to row to place and back. How far off is the place?

A)

3 km


B)

15 km


C)

7 km


D)

16 km



Correct Answer :

3 km


Explanation :

Let the place be x kms from starting point.
Upstream speed = 7.5–1.5=6 kmph
Downstream speed = 7.5+1.5=9 kmph
Time to row up and down = 50/60 hour

Total time=> x/6 + x/9=50/60 hr
5x/18=5/6
5x=15
x=3 km

The place is at distance of 3 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 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

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

Speed of a boat in still water is 10 kmph, and speed of the stream is 5 Kmph. In how many minutes would the boat cover a distance of 5 km downstream?

A)

20 minute


B)

30 minute


C)

40 minute


D)

25 minute



Correct Answer :

20 minute


Explanation :

boat speed = 10 km/hr and stream speed = 5 km/hr
Thus net speed of boat in downstream = 10 + 5 = 15 km/hr

Time taken to travelled 5 km distance

time = distance / speed = 5/ 15 = 1/3 hr = 60/3 minutes = 20 minutes

In one hour, a boat goes 11 km along the stream and 5 km against the stream. The speed of the boat in still water is?

A)

4km/hr


B)

8km/hr


C)

12km/hr


D)

16km/hr



Correct Answer :

8km/hr


Explanation :

Let A= Downstream=11km/hr ,
B=Upstream=5km/hr
Speed in still water = 1/2(A + B) km/hr
= 1/2(11+5)km/hr
= 1/2(16)km/hr
= 8km/hr

A man can row 18 kmph in still water. It takes him thrice as long as row up as to row down the river. find the rate of stream?

A)

4km/hr


B)

8km/hr


C)

9km/hr


D)

12km/hr



Correct Answer :

9km/hr


Explanation :

Let man’s rate upstream be x kmph
then, his rate downstream =3x kmph
Speed in still water, 18 =1/2[3x+x]=2x kmph
x = 9 kmph

Rate upstream, x=9 km/hr,
rate downstream, 3x=27 km/hr
Hence,rate of stream=1/2(27-9)km/hr
=9 km/hr

A man can row 3 quarters of a km against the stream is 11(1/4) min. the speed of the man in still water is?

A)

12 kmph


B)

15 kmph


C)

5 kmph


D)

8 kmph



Correct Answer :

5 kmph


Explanation :

three - quarters of a kilometer = 750 meters
and 11(1/4) minutes= 675 seconds

rate upstream = 750/625 m/sec =10/9 m/sec
rate downstream =750/450 m/sec = 5/3 m/sec
rate in still water =1/2[10/9 + 5/3]
= 25/18 m/sec
= 25/18*18/5 km/hr
= 5 kmph

A boat can travel with a speed of 13 kmph in still water. if the speed of stream is 4 kmph,find the time taken by the boat to go 68 km downstream?

A)

9 hrs


B)

4 hrs


C)

2 hrs


D)

7 hrs



Correct Answer :

4 hrs


Explanation :

Speed down stream = 13+4 = 17 kmph
time taken to travel 68km downstream = 68/17 hrs
= 4 hrs

A boat takes 90 min less to travel 36 miles downstream then to travel the same distance upstream. if the speed of the boat in still water is 10 mph .the speed of the stream is ?

A)

17 mph


B)

12 mph


C)

6 mph


D)

2 mph



Correct Answer :

2 mph


Explanation :

Let the speed of the stream be x mph
then, speed downstream = [10+x]mph
speed upstream =[10-x] mph
90 min= 90/60 hrs

As given, 36/[10-x] - 36/[10+x] = 90/60 hrs
36/[10-x] - 36/[10+x] = 3/2 hrs
36*(10+x)- 36*(10-x) = 3(10+x)(10-x)/2
24*(10+x)- 24*(10-x) = (102-x2)
48x=100-x2
x2+48-100=0
x2+50x−2x−100=0
x(x+50)−2(x+50)=0
(x−2)(x+50)=0
x=−50,2

time cannot be negative.
So, the speed of the stream is 2 mph

At his usual rowing rate, Rahul 12 miles downstream in a certain river in 6 hrs less than it takes him to travel the same distance upstream. but if he could double his usual rowing rate for his 24 miles round the downstream 12 miles would then take only one hour less than the upstream 12 miles. what is the speed of the current in miles per hours?

A)

2(2/3) mph


B)

1(1/3) mph


C)

1(2/3) mph


D)

2/3 mph



Correct Answer :

2(2/3) mph


Explanation :

Let the speed in still water be x mph and the speed of the current be y mph.
then, speed upstream = (x-y)
speed downstream =(x+y)
12/(x-y) - 12/(x+y) = 6
6(x2 - y2) m= 24y
=> x2 - y2 =4y -------(1)
and 12/(2x-y) - 12/(2x+y) =1
4x2 - y2 = 24y
=> x2= ( 24y + y2)/4 -------(2)
from 1 and 2 we have
4y+ y2 =( 24y+y2)/4
y=8/3 mph ie 2(2/3) mph

There is a road beside a river. two friends started from a place A, moved to a temple situated at another place B and then returned to A again. one of them moves on a cycle at a speed of 12 kmph, while the other sails on a boat at a speed of 10 kmph . if the river flows at the speed of 4 kmph , which of the two friends will return to place A first?

A)

Sailor


B)

Cyclist


C)

Both


D)

Data insufficient



Correct Answer :

Cyclist


Explanation :

Clearly, The cyclist moves both ways at a speed of 12 kmph
Average speed of the cyclist = 12 kmph
the boat sailor speed downstream = (10+4) = 14 kmph
speed upstream =(10-4) = 6 kmph
So, average speed of the boat sailor =[ 2*14*6]/[14+6] kmph
=42/5 kmph =8.4 kmph

Since, the average speed of the cyclist is greater 12 kmph> 8.4 kmph
So, the cyclist return to A first.

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