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A man can row 30 km downstream and 20 km upstream in 4 hours. He can row 45 km downstream and 40 km upstream in 7 hours. Find the speed of man in still water?

A.

15kmph

B.

10kmph

C.

12.5 kmph

D.

12kmph

Answer with explanation

Answer: Option CExplanation

Let the speed of the man in still water be a kmph and let the speed of the stream be b kmph.

Now 30/(a + b) + 20/(a – b) = 4 and 45/(a + b) + 40/(a – b) = 7

Solving the equation,

the speed of man in still water is 12.5 kmph.

Workspace

A boat covers 12 km upstream and 18km downstream in 3 hours while it covers 36km upstream and 24 km downstream in 6[1/2] hours, what is the velocity of the stream?

A.

1.5km/hr

B.

2km/hr

C.

3km/hr

D.

2.5km/hr

Answer with explanation

Answer: Option BExplanation

ATQ, Distance in upstream =12km

Distance in downstream = 18 km

Let the speed in upstream = y km/hr

And the speed in downstream = x km/hr

Now, apply the formula.

Time = Distance/ speed

Or, (18/x) + (12/y) = 3………….. (i)

And (24/x) + (36/y) = 13/2……… (ii)

Now, multiply equation i by 3 to equate both equations.

(54/x) + (36/y) = 9………… (iii)

(24/x) + (36/y) = 13/2…….. (iv)

Now subtract equation iii by iv.

30/x = 9-13/2

Or, 30/x = 5/2

Or, 5x=60, i.e., x = 12

Now, put the value of x in equation i

(18/12) + (12/y) = 3

Or, 3/2 + 12/y = 3

Or, 12/y = 3-3/2

Or, 12/y = 3/2

Or, y = 8km/hr

Now, velocity of stream = (x-y)/ 2

= (12-8)/ 2 = 2 km/hr.

Workspace

A man can swim at 5 km per hour velocity in still water. He takes 75 minutes to swim from position A to the position B and back in a river when it is flowing at 1 km per hour. The distance between A and B is?

A.

3 km

B.

8 km

C.

9 km

D.

15 km

Answer with explanation

Answer: Option AExplanation

Workspace

Speed of a boat in standing water is 9 kmph and the speed of the stream is 1.5 kmph. A man rows to a place at a distance of 105 km and comes back to the starting point. The total time taken by him is:

A.

18

B.

20

C.

24

D.

35

Answer with explanation

Answer: Option CExplanation

Speed upstream = 7.5 kmph.

Speed downstream = 10.5 kmph.

Total time taken =105/7.5 +105/10.5 hours = 24 hours.

Workspace

The speed of a boat in still water is 60kmph and the speed of the current is 20kmph. Find the speed downstream and upstream?

A.

35,25kmph

B.

80,40kmph

C.

40,60kmph

D.

50,55kmph

Answer with explanation

Answer: Option BExplanation

Speed downstream = 60 + 20 = 80 kmph

Speed upstream = 60 – 20 = 40 kmph

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.

2:1

B.

3:1

C.

5:6

D.

9:5

Answer with explanation

Answer: Option BExplanation

Workspace

A.

16 km

B.

30 km

C.

42 km

D.

70 km

Answer with explanation

Answer: Option CExplanation

Workspace

If athul rows 16 km upstream and 24 km down steam taking 4 hours each, then the speed of the

A.

1kmph

B.

2 kmph

C.

1.5 kmph

D.

12 kmph

Answer with explanation

Answer: Option AExplanation

Speed upstream = 16/4 = 4 kmph

Speed down stream = 24/4 = 6 kmph

Speed of stream = ½ (6-4) = 1 kmph

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 boat covers a certain distance downstream in 1 hour, while it comes back in 1 hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?

A.

13 kmph

B.

4 kmph

C.

14 kmph

D.

15 kmph

Answer with explanation

Answer: Option DExplanation

Workspace

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

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