Aptitude

Question:
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

Question: The speed of a boat in still water in 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

Answer: Option D

Explanation:

Speed downstream = (15 + 3) kmph = 18 kmph.

Distance travelled =		18 x	12	km = 3.6 km.
			60

Video Explanation: https://youtu.be/IDOwWUeOldQ

Question:
A boat can travel with a speed of 13 km/hr in still water. If the speed of the stream is 4 km/hr, find the time taken by the boat to go 68 km downstream.

[A].

2 hours

[B].

3 hours

[C].

4 hours

[D].

5 hours

Answer: Option C

Explanation:

Speed downstream = (13 + 4) km/hr = 17 km/hr.

Time taken to travel 68 km downstream =		68	hrs = 4 hrs.
		17

Question:
A man’s speed with the current is 15 km/hr and the speed of the current is 2.5 km/hr. The man’s speed against the current is:

[A].

8.5 km/hr

[B].

9 km/hr

[C].

10 km/hr

[D].

12.5 km/hr

Answer: Option C

Explanation:

Man’s rate in still water = (15 – 2.5) km/hr = 12.5 km/hr.

Man’s rate against the current = (12.5 – 2.5) km/hr = 10 km/hr.

Question:
A boat running upstream takes 8 hours 48 minutes to cover a certain distance, while it takes 4 hours to cover the same distance running downstream. What is the ratio between the speed of the boat and speed of the water current respectively?

[A].

2 : 1

[B].

3 : 2

[C].

8 : 3

[D].

Cannot be determined

Answer: Option C

Explanation:

Let the man’s rate upstream be x kmph and that downstream be y kmph.

Then, distance covered upstream in 8 hrs 48 min = Distance covered downstream in 4 hrs.

		x x 8	4		= (y x 4)
			5

	44	x =4y
	5

y =	11	x.
	5

Required ratio =		y + x		:		y – x
		2				2

=		16x	x	1		:		6x	x	1
		5		2				5		2

=	8	:	3
	5		5

   = 8 : 3.

Question:
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.

Question: 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.

Question: A boat running downstream covers a distance of 16 km in 2 hours while for covering the same distance upstream, it takes 4 hours. What is the speed of the boat in still water?
[A].

4 km/hr

[B].

6 km/hr

[C].

8 km/hr

[D].

Data inadequate

Answer: Option B

Explanation:

Rate downstream =		16	kmph = 8 kmph.
		2

Rate upstream =		16	kmph = 4 kmph.
		4

Speed in still water =	1	(8 + 4) kmph = 6 kmph.
	2

Video Explanation: https://youtu.be/3D8uAfzz3l0

Question: In one hour, a boat goes 11 km/hr along the stream and 5 km/hr against the stream. The speed of the boat in still water (in km/hr) is:
[A].

3 km/hr

[B].

5 km/hr

[C].

8 km/hr

[D].

9 km/hr

Answer: Option C

Explanation:

Speed in still water =	1	(11 + 5) kmph = 8 kmph.
	2

Video Explanation: https://youtu.be/KQX_mA3tcVA