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A man rows to a place 48 km distant and come back in 14 hours. He finds that he can row 4 km with the stream in the same time as 3 km against the stream. The rate of the stream is:

A.

1 km/hr.

B.

2 km/hr.

C.

1.5 km/hr.

D.

2.5 km/hr.

Answer with explanation

Answer: Option AExplanation

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.

700 hours

B.

350 hours

C.

1400 hours

D.

1010 hours

Answer with explanation

Answer: Option AExplanation

Speed downstream = (14 + 1.2) = 15.2 kmph Speed upstream = (14 – 1.2) = 12.8 kmph Total time taken = 4864/ 15.2 + 4864/ 12.8 = 320 + 380 = 700 hours

Workspace

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.

3 : 1

B.

1 : 3

C.

1 : 2

D.

2 : 1

Answer with explanation

Answer: Option AExplanation

Workspace

A boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream. If the speed of the boat in still water is 10 mph, the speed of the stream is:

A.

4 mph

B.

2.5 mph

C.

3 mph

D.

2 mph

Answer with explanation

Answer: Option DExplanation

Workspace

A Cistern is filled by pipe A in 8 hrs and the full Cistern can be leaked out by an exhaust pipe B in 12 hrs. If both the pipes are opened in what time the Cistern is full?

A.

12 hrs

B.

24 hrs

C.

16 hrs

D.

32 hrs

Answer with explanation

Answer: Option BExplanation

Pipe A can fill ^{1}⁄_{8} of the cistern in 1 hour.

Pipe B can empty ^{1}⁄_{12} of the cistern in 1 hour

Both Pipe A and B together can effectively fill ^{1}⁄_{8}–^{1}⁄_{12}= ^{1}⁄_{24} of the cistern in 1 hour

i.e, the cistern will be full in 24 hrs.

Workspace

Two pipes A and B can fill a tank in 10 hrs and 40 hrs respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?

A.

8 hours

B.

6 hours

C.

4 hours

D.

2 hours

Answer with explanation

Answer: Option AExplanation

Pipe A can fill ^{1}⁄_{10} of the tank in 1 hr

Pipe B can fill ^{1}⁄_{40} of the tank in 1 hr

Pipe A and B together can fill ^{1}⁄_{10} + ^{1}⁄_{40} = ^{1}⁄_{8} of the tank in 1 hr

i.e., Pipe A and B together can fill the tank in 8 hours

Workspace

A.

2 and 1/3 mph

B.

1 and 1/3 mph

C.

1 and 2/3 mph

D.

2 and 2/3 mph

Answer with explanation

Answer: Option DExplanation

Workspace

A boatman can row 96 km downstream in 8 hr. If the speed of the current is 4 km/hr, then find in what time will be able to cover 8 km upstream?

A.

6 hr

B.

2 hr

C.

4 hr

D.

1 hr

Answer with explanation

Answer: Option BExplanation

Speed in downstream = 96/8 = 12 kmph

Speed of current = 4 km/hr

Speed of the boatman in still water = 12 – 4 = 8 kmph

Speed in upstream = 8 – 4 = 4 kmph

Time taken to cover 8 km upstream = 8/4 = 2 hours.

Workspace

A man can row at a speed of 12 km/hr in still water to a certain upstream point and back to the starting point in a river which flows at 3 km/hr. Find his average speed for total journey

A.

6.8km/h

B.

5.8km/h

C.

4.5km/h

D.

4.8km/h

Answer with explanation

Answer: Option DExplanation

downstream speed =12-3=9km/h

avg speed = 2*12*3/(12+3)

= 4.8km/h

Workspace

A boat takes 38 hours for travelling downstream from point A to point B and coming back to point C midway between A and B. If the velocity of the stream is 4 kmph and the speed of the boat in still water is 14 kmph, what is the distance between A and B?

A.

240 km

B.

120 km

C.

360 km

D.

180 km

Answer with explanation

Answer: Option CExplanation

Workspace

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.

10 km/hr

C.

12.5 km/hr

D.

9 km/hr

Answer with explanation

Answer: Option BExplanation

Man’s speed with the current = 15 km/hr

=> speed of the man + speed of the current = 15 km/hr

speed of the current is 2.5 km/hr

Hence, speed of the man = 15 – 2.5 = 12.5 km/hr

man’s speed against the current = speed of the man – speed of the current

= 12.5 – 2.5 = 10 km/hr

Workspace

A man rows 750 m in 675 seconds against the stream and returns in 7 and half minutes. His rowing speed in still water is

A.

4 kmph

B.

5 kmph

C.

6 kmph

D.

7 kmph

Answer with explanation

Answer: Option BExplanation

Rate upstream = (750/675) = 10/9 m/sec

Rate downstream (750/450) m/sec = 5/3 m/sec

Rate in still water = (1/2)*[(10/9) + (5/3)] m/sec.

= 25/18 m/sec

= (25/18)*(18/5) kmph

= 5 kmph

Workspace

A boat can travel with a speed of 16 km/hr in still water. If the rate of stream is 5 km/hr, then find the time taken by the boat to cover distance of 84 km downstream.

A.

4 hours

B.

5 hours

C.

6 hours

D.

7 hours

Answer with explanation

Answer: Option AExplanation

It is very important to check, if the boat speed given is in still water or with water or against water. Because if we neglect it we will not reach on right answer. I just mentioned here because mostly mistakes in this chapter are of this kind only.

Lets see the question now.

Speed downstream = (16 + 5) = 21 kmph

Time = distance/speed = 84/21 = 4 hours

Workspace

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