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A man can row 9 (1/3) kmph in still water and finds that it takes him thrice as much time to row up than as to row down the same distance in the river. What is speed of the current ?

A.

3(1/2) km/hr

B.

5km/hr

C.

8 (3/2)km/hr

D.

4 (2/3) km/hr

Answer with explanation

Answer: Option DExplanation

Let man’s rate upstream be x km/hr. Then his rate downstream is 3 x km/hr

Given:

Speed in still water = 9 (1/3) = 28/3 km/hr

i.e, ½ (a+b) = 28/3 km/hr

½ (x+3x) = 28/3

2x = 28/3 x = 28/ 2 x 3 = 14/3 km/hr

rate upstream b = 14/3 km/hr and

rate downstream a = 14/3 x 3 = 14 km/hr

speed of the current = ½ (a-b) = ½ (14 – 14/3)

= ½ (42-14/3) = 28/6 = 4 (2/3) km/hr

Workspace

The speed of the boat in still water is 5 times that of current, it takes 1.1 hour to row to point B from point A downstream. The distance between point A and point B is 13.2 km. How much distance (in km) will it cover in 312 minutes upstrem?

A.

43.2

B.

48

C.

41.6

D.

44.8

Answer with explanation

Answer: Option CExplanation

Workspace

A boat takes half time in moving a certain distance downstream than upstream. What is the ratio between the rate in still water and rate of current?

A.

1 : 2

B.

3 : 1

C.

2 : 1

D.

1 : 3

Answer with explanation

Answer: Option BExplanation

Let the speed of the boat in still water be 4 km/hr and speed of the current be u km/hr.

Rate downstream = (u + v) km/hr.

Rate upstream = (u- v)km/hr

Let the distance covered in each case be x km.

Then 2x/(u + v) = x / (u – v)

=> 2 (u – v) = ( u + v)

=> u =3v

=> u/v =3/1

Workspace

A man rows ‘k’ km upstream and back again downstream to the same point in H hours. The speed of rowing in still water is s km/hr and the rate of stream is r km/hr. Then?

A.

(r + s) = kH / (r -s)

B.

(s^{2}-r^{2}) =2sk /H

C.

rs = kH

D.

None of the above

Answer with explanation

Answer: Option BExplanation

Time taken to cover total distance = H hrs.

Speed of upstream = s – r. Speed of downstream = s + r.

∴ k / (s + r) + k / (s – r) = H ⇒(s^{2}-r^{2}) =2sk /H

Workspace

A boat covers a certain distance downstream in 2 hour, while it comes back in 2 1/2 hours. If the speed of the stream be 5 kmph, what is the speed of the boat in still water?

A.

45 kmph

B.

35 kmph

C.

30 kmph

D.

40 kmph

Answer with explanation

Answer: Option AExplanation

Let the speed of the boat in still water be *x* kmph. Then,

Speed downstream = (*x* + 5) kmph,

Speed upstream = (*x* – 5) kmph.

(*x* + 5)*2 = (*x* – 5)*5/2

X = 45 kmph

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 he will be able to cover 8 km upstream?

A.

1.5 hrs

B.

1 hrs

C.

2.5 hrs

D.

2 hrs

Answer with explanation

Answer: Option DExplanation

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.

5 km/hr

B.

3 km/hr

C.

7 km/hr

D.

9 km/hr

Answer with explanation

Answer: Option CExplanation

Let x be speed of u / s and y be the speed of d / s.

∴ (16/x) + (16/y) = (28/5) and 16/(y+2) + 16/(x-2) = 28/3

Solving these 2 equations, we get x = 4km/hr and y = 10km/hr

∴ speed of boat in still water = (4+10) / 2 = 7km/hr.

Workspace

A man rows to a place 40 km distant and come back in 9 hours. He finds that he can row 5 km with the stream in the same time as 4 km against the stream. The rate of the stream is:

A.

1 km/hr

B.

1.5 km/hr

C.

2 km/hr

D.

2.5 km/hr

Answer with explanation

Answer: Option AExplanation

Speed downstream = 5/x

Speed upstream = 4/x

40/(5/x) + 40/(4/x) = 9

X = ½

So, Speed downstream = 10 km/hr, Speed upstream = 8 km/hr.

Rate of the stream = 1/2 * 2 = 1 kmph

Workspace

The ratio of the speed of boat in still water to the speed of stream is 16 : 5. A boat goes 16.5 km in 45 minute upstream, find the time taken by boat to cover the distance of 17.5 km downstream.

A.

25 minutes

B.

30 minutes

C.

50 minutes

D.

45 minutes

Answer with explanation

Answer: Option AExplanation

Let the speed of boat in still water = 16x, speed of stream = 5x

Upstream speed = 16x – 5x = 11x

S = D/t

11x = (16.5 × 60)/45

x = 2

speed of boat in still water = 32 km/h, speed of stream = 10 km/h

Downstream speed = 32 + 10 = 42 km/h

Distance = 17.5 km

time = 17.5/42

= 5/12 hour

or( 5/12 )× 60 = 25 minutes

Workspace

Speed of a man in still water is 5 km/hr and the river is running at 3km/hr. The total time taken to go to a place and come back is 10 hours. What is the distance travelled?

A.

36 km

B.

32 km

C.

24 km

D.

10 km

Answer with explanation

Answer: Option BExplanation

Down speed= 5+3= 8

Up speed= 5-3=2

Let distance travelled = X

(X/8)+(X/2)= 10

X= 16 km

Total distance is 16+16=32

Workspace

A man goes down stream with a boat to some destination and returns upstream to his original place in 5 hours. If the speed of the boat in still water and the strean are 10km/hr and 14km/hr respectively, the distance of the destination from the string place is?

A.

16 km

B.

18 km

C.

21 km

D.

25 km

Answer with explanation

Answer: Option CExplanation

Workspace

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