Boats and Streams - Aptitude Questions and Answers - geeksorgeeks

Boats and Streams - Important Formulas

1.  Downstream/Upstream:

In water, the direction along the stream is called downstream. And, the direction against the stream is called upstream.

2. If the speed of a boat in still water is u km/hr and the speed of the stream is v km/hr, then:

Speed downstream = (u + v) km/hr.

Speed upstream = (u - v) km/hr.

3. If the speed downstream is a km/hr and the speed upstream is b km/hr, then:

Speed in still water =	1	(a + b) km/hr.
	2

Rate of stream =	1	/2(a - b) km/hr

 

 

1. 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 & Explanation

Answer: Option C

Explanation:

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

Time taken to travel 68 km downstream =(68/17) hrs = 4 hrs

2. 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 & Explanation

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.

3. 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 & Explanation

Answer: Option C

Explanation:

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

4. 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 & Explanation

Answer: Option B

Explanation:

Rate downstream = (16/2) kmph = 8 kmph

Rate upstream = (16/4) kmph = 4 kmph.

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

5. 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 & Explanation

Answer: Option D

Explanation:

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

Distance travelled = (18 x12/60) km = 3.6 km.

6.

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.12.5km/hr Answer & Explanation 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. 7.  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. 3km/h                B.5km/h C. 8km/h                D. 9km/h Answer & Explanation Answer: Option C Explanation: Speed in still water=1/2(11+5)kmph=8kmph 8.  What is the speed of the boat in still water? I.  The boat covers a distance of 48 kms in 6 hours while running upstream.  II.  The boat covers the same distance in 4 hours while running downstream. A. I alone sufficient while II alone not sufficient to answer B. II alone sufficient while I alone not sufficient to answer C. Either I or II alone sufficient to answer D. Both I and II are not sufficient to answer E. Both I and II are necessary to answer Answer: Option E Explanation:  I. Speed upstream = 48 km/hr = 8 km/hr. 6 II. Speed downstream = 48 km/hr = 12 km/hr. 4 Speed of the boat = 1 (8 + 12) km/hr = 10 km/hr. 2 Thus, I and II together give the answer. ∴Correct answer is (E).

 

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