Boats and Streams ( 6 to 10 )

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APTITUDE QUESTIONS (BOATS AND STREAMS):

6. A woman takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. What is the ratio of the speed of the boat (in still water) and the stream?


A)    2:1

B)    3:1

C)    3:2

D)    4:3

E)    None of these

View Answer

Answer: option (B)

Explanation:

Let woman’s rate upstream be x kmph. Then, her rate downstream = 2x kmph
∴ (Speed in still water) : (Speed of stream) = ((2x+x)/2) : ((2x-x)/2) = 3x/2 : x/2 = 3:1

 

7. 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)    4:3

E)    None of these

View Answer

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 mins. = Distance covered downstream in 4 hrs.
(x*8(4/5)) = (y * 4) => (44/5)x = 4y => (11/5)x
∴ Required ratio = ((y+x)/2) : ((y – x)/2) = (16x/5*1/2) : (6x/5*1/2) = 8/5 : 3/5 = 8:3

 

8. If a boat goes 7 km upstream in 42 minutes and the speed of the stream is 3 kmph, then the speed of the boat in still water is:

A)    4.2 km/hr


B)    9 km/hr

C)    13 km/hr

D)    21 km/hr

E)    None of these

View Answer

Answer: option (C)

Explanation:

Rate upstream = (7/42*60) kmph = 10 kmph
Speed of stream = 3 kmph
Let speed in still water be a km/hr. Then, speed upstream = (a – 3) km/hr.
∴ a – 3 = 10 or a = 13 km/hr

 

9. 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

E)    None of these

View Answer

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) = 10 km/hr

 

10. If a man rows at the rate of 5 kmph in still water and his rate against the current is 3.5 km/hr, then the man’s rate along the current is:

A)    4.25 km/hr

B)    6 km/hr

C)    6.5 km/hr

D)    8.5 km/hr

E)    None of these

View Answer

Answer: option (C)

Explanation:

Let the rate along the current be x kmph. Then, 1/2 (x + 3.5) = 5 or x = 6.5 km/hr

 

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