Boats and Streams

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Boats and Streams:


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

  • 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 of downstream = (u + v) km/hr
    Speed of upstream = (u – v) km/hr
  • If the speed downstream is a km/hr and the speed upstream is b km/hr, then:
    Speed in still water = 1/2 (a + b) km/hr
    Rate of stream = 1/2 (a – b) km/hr

Aptitude Questions (Boats and Streams):

1. In one hour, a boat goes 11 km along the stream and 5 km against the stream. What is the speed of the boat in still water (in km/hr)?

A)    3

B)    5

C)    8

D)    9

E)    None of these

View Answer

Answer: option (C)

Explanation:

Speed in still water = 1/2 (11 + 5) km/hr = 8 km/hr

 

2. A woman can row upstream at 6 kmph and downstream at 12 kmph. The speed of the stream is:

A)    3 km/hr

B)    4.2 km/hr

C)    5 km/hr

D)    10.5 km/hr

E)    None of these

View Answer

Answer: option (A)

Explanation:

Speed of stream = 1/2 (12 – 6) km/hr = 3 km/hr

 

3. A man rows downstream 32 km and 14 km upstream. If he takes 9 hours to cover each distance, then the velocity (in kmph) of the current is:

A)    1/2


B)    1

C)    1.5

D)    2

E)    None of these

View Answer

Answer: option (B)

Explanation:
Rate of downstream = (32/9) kmph; Rate of upstream = (14/9) kmph
∴ Velocity of current = 1/2 (32/9-14/9 ) kmph = 2/2 kmph = 1kmph

 

4. A boat running downstream covers a distance of 24 km in 2 hours while for covering the same distance upstream, it takes 4 hours. What will be the speed of the boat in still water?

A)    4 km/hr

B)    9 km/hr

C)    8 km/hr

D)    10 km/hr

E)    None of these

View Answer

Answer: option (B)

Explanation:

Rate of downstream = (24/2) kmph = 12 kmph; Rate of upstream = (24/4) kmph = 6 kmph
∴ Speed in still water = 1/2 (12 + 6) kmph = 9 kmph

 

5. A boatman goes 2km 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 stationery water?

A)    40 minutes

B)    1 hour

C)    1 hr 15 min

D)    1 hr 30 min

E)    None of these

View Answer

Answer: option (C)

Explanation:

Rate of downstream = (1/10*60) km/hr = 6 km/hr; Rate of upstream = 2 km/hr
Speed in still water = 1/2 (6 + 2) kmph = 4 kmph
∴ Required time = (5/4) hrs = 1 hr 15 mins

 

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