Aptitude - Boats and Streams

Exercise :: Boats and Streams - General Questions

11. 

A boatman goes 2 km against the current of the stream in 1 hour and goes 1 km along the current in 10 minutes. How long will it take to go 5 km in stationary water?

A. 40 minutes
B. 1 hour
C. 1 hr 15 min
D. 1 hr 30 min

Answer: Option C

Explanation:

Rate downstream = 1 x 60 km/hr = 6 km/hr.
10

Rate upstream = 2 km/hr.

Speed in still water = 1 (6 + 2) km/hr = 4 km/hr.
2

Required time = 5 hrs = 1 1 hrs = 1 hr 15 min.
4 4


12. 

A man can row three-quarters of a kilometre against the stream in 11 minutes and down the stream in 7 minutes. The speed (in km/hr) of the man in still water is:

A. 2
B. 3
C. 4
D. 5

Answer: Option D

Explanation:

We can write three-quarters of a kilometre as 750 metres,

and 11 minutes as 675 seconds.

Rate upstream = 750 m/sec = 10 m/sec.
675 9

Rate downstream = 750 m/sec = 5 m/sec.
450 3

Rate in still water = 1 10 + 5 m/sec
2 9 3

   = 25 m/sec
18

   = 25 x 18 km/hr
18 5

   = 5 km/hr.


13. 

Speed of a boat in standing water is 9 kmph and the speed of the stream is 1.5 kmph. A man rows to a place at a distance of 105 km and comes back to the starting point. The total time taken by him is:

A. 16 hours
B. 18 hours
C. 20 hours
D. 24 hours

Answer: Option D

Explanation:

Speed upstream = 7.5 kmph.

Speed downstream = 10.5 kmph.

Total time taken = 105 + 105 hours = 24 hours.
7.5 10.5


14. 

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 the stream is:

A. 2 : 1
B. 3 : 1
C. 3 : 2
D. 4 : 3

Answer: Option B

Explanation:

Let man's rate upstream be x kmph.

Then, his rate downstream = 2x kmph.

(Speed in still water) : (Speed of stream) = 2x + x : 2x - x
2 2

   = 3x : x
2 2

   = 3 : 1.


15. 

A man rows to a place 48 km distant and come back in 14 hours. He finds that he can row 4 km with the stream in the same time as 3 km against the stream. The rate of the stream is:

A. 1 km/hr
B. 1.5 km/hr
C. 2 km/hr
D. 2.5 km/hr

Answer: Option A

Explanation:

Suppose he move 4 km downstream in x hours. Then,

Speed downstream = 4 km/hr.
x

Speed upstream = 3 km/hr.
x

48 + 48 = 14 or x = 1 .
(4/x) (3/x) 2

So, Speed downstream = 8 km/hr, Speed upstream = 6 km/hr.

Rate of the stream = 1 (8 - 6) km/hr = 1 km/hr.
2


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