Boats And Streams

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: B

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.

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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: D

Speed upstream = 7.5 kmph.

Speed downstream = 10.5 kmph.

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

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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: D

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.

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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: C

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

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A boat covers a certain distance downstream in 1 hour, while it comes back in 1

hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?

A:

12 kmph

B:

13 kmph

C:

14 kmph

D:

15 kmph

Answer: D

Let the speed of the boat in still water be x kmph. Then,

Speed downstream = (x + 3) kmph,

Speed upstream = (x - 3) kmph.

(x + 3) x 1 = (x - 3) x	3
	2

2x + 6 = 3x - 9

x = 15 kmph.

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Questions for: Boats And Streams