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A Learning Portal from Recruitment India

A boat sails 15 km of a river towards upstream in 5 hrs. How long will it take to cover the same distance downstream, if the speed of current is one-fourth the speed of the boat in still water:

A.

5 hrs

B.

3 hrs

C.

1.5 hrs

D.

4 hrs

Answer with explanation

Answer: Option BExplanation

Upstream Speed = B – S

Downstream Speed = B + S

Workspace

Speed of a boat in standing water is 14 kmph and the speed of the stream is 1.2 kmph. A man rows to a place at a distance of 4864 km and comes back to the starting point. The total time taken by him is:

A.

1010 hours

B.

1400 hours

C.

700 hours

D.

350 hours

Answer with explanation

Answer: Option CExplanation

Speed downstream = (14 + 1.2) = 15.2 kmph

Speed upstream = (14 – 1.2) = 12.8 kmph

Workspace

If Rahul rows 15 km upstream in 3 hours and 21 km downstream in 3 hours, then the speed of the stream is

A.

1 kmph

B.

2 kmph

C.

3 kmph

D.

4 kmph

Answer with explanation

Answer: Option AExplanation

Rate upstream = (15/3) kmph

Rate downstream (21/3) kmph = 7 kmph.

Speed of stream (1/2)(7 – 5)kmph = 1 kmph

Workspace

A boy can swim in still water at 4.5 km/hr, but takes twice as long to swim upstream than downstream. The speed of the stream is?

A.

1.2 kmph

B.

1.5 kmph

C.

1.7 kmph

D.

2.0 kmph

Answer with explanation

Answer: Option BExplanation

Speed of Boy is B = 4.5 kmph

Let the speed of the stream is S = x kmph

Then speed in Down Stream = 4.5 + x

speed in Up Stream = 4.5 – x

As the distance is same,

=> 4.5 + x = (4.5 – x)2

=> 4.5 + x = 9 -2x

3x = 4.5

x = 1.5 kmph

Workspace

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