A Learning Portal from Recruitment India

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

The speed of a boat in still water is 15 km/hr and the rate of current is 3 km/hr. The distance travelled downstream in 12 minutes is

A.

1.6 km

B.

2 km

C.

3.6 km

D.

4 km

Answer with explanation

Answer: Option CExplanation

Speed downstreams =(15 + 3)kmph

= 18 kmph.

Distance travelled = (18 x 12/60)km

= 3.6km

Workspace

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

A.

1.8 kmph

B.

2 kmph

C.

2.2 kmph

D.

1.5 kmph

Answer with explanation

Answer: Option DExplanation

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

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

A.

1.8h

B.

3h

C.

4h

D.

5h

Answer with explanation

Answer: Option BExplanation

Upstream speed = B-S

Downstream speed = B+s

B-S = 15/5 = 3 km/h

Again B= 4S

Therefore B-S = 3= 3S

=> S = 1 and B= 4 km/h

Therefore B+S = 5km/h

Therefore, Time during downstream = 15/5 = 3h

Workspace

In one hour, a boat goes 12 km/hr along the stream and 6 km/hr against the stream. The speed of the boat in still water (in km/hr) is:

A.

9

B.

8

C.

7

D.

7.5

Answer with explanation

Answer: Option AExplanation

Speed in still water = Average of Speed in Upstream and speed in Downstream

= 1/2 (12 + 6) kmph = 9 kmph.

Workspace

A man can row 8 kmh in still water. If the river is running at 2 kmh, it takes 4 hrs more upstream than to go downstream for the same distance. Then the distance is given by

A.

54 kms

B.

32 kms

C.

45 kms

D.

60 kms

Answer with explanation

Answer: Option DExplanation

Workspace

A boatman can row 3 km against the stream in 20 minutes and return in 18 minutes. Find the rate of current ?

A.

1/3 kmph

B.

2/3 kmph

C.

1/4 kmph

D.

1/2 kmph

Answer with explanation

Answer: Option DExplanation

Speed in upstream = Distance / Time = 3 x 60/20 = 9 km/hr.

Speed in downstream = 3 x 60/18 = 10 km/hr

Rate of current = (10-9)/2 = 1/2 km/hr.

Workspace

A boat takes 2 hours to travel from point A to B in still water. To find out its speed upstream, which of the following information is/are required?

1. Distance between point A and B.

2. Time taken to travel downstream from B to A.

3. Speed of the stream of water.

A.

Only A and B

B.

Only B and C

C.

All are required

D.

Any one pair of A and B, B and C or C and A is sufficient

Answer with explanation

Answer: Option DExplanation

Let distance between A & B = d km

Let speed in still water = x kmph

Let speed of current = y kmph

from the given data,

d/x = 2

From 1) we get d

From 2) we get d/x+y

From 3) we get y

So, Any one pair of A and B, B and C or C and A is sufficient to give the answer i.e, the speed of upstream.

Workspace

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.

7:4

B.

11:4

C.

4:7

D.

8:3

Answer with explanation

Answer: Option DExplanation

Let the speed of the boat upstream be p kmph and that of downstream be q kmph

Time for upstream = 8 hrs 48 min = 845845hrs

Time for downstream = 4 hrs

Distance in both the cases is same.

=> p x 845845= q x 4

=> 44p/5 = 4q

=> q = 11p/5

Now, the required ratio of Speed of boat : Speed of water current

= q+p2:q−p2q+p2:q-p2

=> (11p/5 + p)/2 : (11p/5 – p)/2

=> 8 : 3

Workspace

A motorboat 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 motorboat and speed of the water current respectively?

A.

3:7

B.

7:9

C.

5:4

D.

8:3

Answer with explanation

Answer: Option DExplanation

Workspace

A motorboat goes 8 km an hour in still water, but takes thrice as much time in going the same distance against the current than going with the current. Then find the speed of the current?

A.

4 kmph

B.

6 kmph

C.

3 kmph

D.

2 kmph

Answer with explanation

Answer: Option AExplanation

Let the speed of current = **‘C’** km/hr

Given the speed of boat in still water = 6 kmph

Let **‘d’** kms be the distance it covers.

According to the given data,

Boat takes thrice as much time in going the same distance against the current than going with the current

Workspace

Find the speed of stream if a boat covers 36 km in downstream in 6 hours which is 3 hours less in covering the same distance in upstream?

A.

1.5 kmph

B.

1 kmph

C.

0.75 kmph

D.

0.5 kmph

Answer with explanation

Answer: Option BExplanation

Speed of the boat upstream = 36/9 = 4 kmph

Speed of the boat in downstream = 36/6 = 6 kmph

Speed of stream = 6-4/2 = 1 kmph

Workspace

The speed of a boat in still water is 8 kmph. If it can travel 1 km upstream in 1 hr, what time it would take to travel the same distance downstream?

A.

1 minute

B.

2 minutes

C.

3 minutes

D.

4 minutes

Answer with explanation

Answer: Option DExplanation

Speed of the boat in still water = 8 km/hr

Speed upstream =11=11 = 1 km/hr

Speed of the stream = 8-1 = 7 km/hr

Speed downstream = (8+7) = 15 km/hr

Time taken to travel 1 km downstream =115 hr = 1×6015= 4 minutes

Workspace

The speed of a boat in still water is 25 kmph. If it can travel 10 km upstream in 1 hr, what time it would take to travel the same distance downstream?

A.

22 minutes

B.

30 minutes

C.

40 minutes

D.

15 minutes

Answer with explanation

Answer: Option DExplanation

Speed of boat in still water = 25 km/hr

Speed upstream =101=101 = 10 km/hr

Speed of the stream = (25-10) = 15 km/hr

Speed downstream = (25+15) = 40 km/hr

Time taken to travel 10 km downstream =1040 hours=10×6040=1040 hours=10×6040 = 15 minutes

Workspace

If a man’s rate with the current is 15 km/hr and the rate of the current is 11⁄2 km/hr, then his rate against the current is

A.

12 km/hr

B.

10 km/hr

C.

10.5 km/hr

D.

12.5 km/hr

Answer with explanation

Answer: Option AExplanation

Speed downstream = 15 km/hr

Rate of the current= 1^{1}⁄_{2} km/hr

Speed in still water = 15 – 1^{1}⁄_{2} = 13^{1}⁄_{2} km/hr

Rate against the current = 13^{1}⁄_{2} km/hr – 1^{1}⁄_{2} = 12 km/hr

Workspace

Correct Answer 👍

Wrong Answer 👎