Boat and Stream Questions and answers

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Aptitude

11). A man can row 5 km per hour in still water. If the river is flowing at 1km per hour, it takes him 75 minutes to row to a place and back. How far is the place?

A). 3 km

B). 2.5 km

C). 4 km

D). none of these

View Answer

12). Speed of a boat in still water is 7 km/hr and speed of the stream is 1.5 km/hr . How much time will it take to move up is stream of a distance 7.7 km?

A). 75 minutes

B). 84 minutes

C). 72 minutes

D). none of these

View Answer

13). A motorboat takes 2 hours to travel a distance of 9 km down the current and it takes 6 hours to travel the same distance against the current. What is the speed of the boat in still water in kmph?

A). 3

B). 2

C). 1.5

D). 1

View Answer

Correct Answer: 3

Let the speed of boat in still water and speed of current are x and y km/h respectively.

Therefore Downward speed of boat = (x+y) km/h.

According to question,

\( \Large x + y = \frac{9}{2} = 2x + 2y = 9 \) ...(i)

and \( \Large x - y = \frac{9}{6} = 2x - 2y = 3 \) ...(ii)

On solving equations (i) and (ii), we get

x = 3, y = \( \Large \frac{3}{2} \)

14). When the speed of a boat in still water is 4 km/h and the rate of stream is 2 km/h, find upstream speed of the boat.

A). 6 km/h

B). 5 km/h

C). 2 km/h

D). 7 km/h

View Answer

15). If the speed of a swimmer in still water is 9 km/h. Find the downstream speed of the swimmer, when the river is flowing with the speed of 6 km/h.

A). 15 km/h

B). 18 km/h

C). 3 km/h

D). 12 km/h

View Answer

16). Ravi can row downstream at 9 km/h and upstream at 5 km/h. Find the speed of Ravi in still water and speed of current.

A). 7 km/h and 2 km/h

B). 8 km/h and 6 km/h

C). 7 km/h and 3 km/h

D). 8 km/h and 2 km/h

View Answer

Correct Answer: 7 km/h and 2 km/h

Given, downstream speed = 9 km/h

and upstream speed = 5 km/h

According to the formula,

Ravi's speed in still water

= \( \Large \frac{1}{2} \) (Speed downstream + Speed upstream)

= \( \Large \frac{1}{2} \) (9 + 5) = \( \Large \frac{14}{2 }\) = 7 km/h

and speed of current

= \( \Large \frac{1}{2} \) (Speed downstream - Speed upstream)

= \( \Large \frac{1}{2} \) (9 -5) = \( \Large \frac{4}{2} \) = 2 km/h

17). A swimmer's speed downstream is 11 km/h and speed of the stream is 1.5 km/h. Find the upstream speed of swimmer.

A). 8 km/h

B). 9.5 km/h

C). 9 km/h

D). 6.25 km/h

View Answer

Correct Answer: 8 km/h

Given, rate of stream = 1.5 km/h

We know that,

Rate of stream = \( \Large \frac{1}{2} \) (Speed downstream - Speed upstream)

=> 1.5 = \( \Large \frac{1}{2} \left(11-Speed \ upstream\right) \)

=> 11 - Speed upstream = 3

Therefore, Speed upstream => 11 - 3 = 8 km/h

18). A boatman rows 1 km in 5 min along the stream and 6 km in 1 h against the stream. The Speed of the stream is

A). 3 km/h

B). 6 km/h

C). 10 km/h

D). 12 km/h

View Answer

Correct Answer: 3 km/h

Let the speed of boat and stream be x and y km/h.

Therefore, Speed of boat along stream = (x + y) km/h

and Speed of boat against stream = (x - y) km/h

According to the question,

x + y = \( \Large \frac{1}{\frac{5}{60}} = \frac{60}{5} \)

= x + y = 12 ...(i)

and x-y = 6 ..(ii)

On adding Eqs. (i) and (ii), we get

2x = 18

x = \( \Large \frac{18}{2} \) = 9

On Putting the value of x in Eq. (i), we get

9 + y = 12

y = 12 - 9 = 3

Hence, speed of boat = 9 km/h

and speed of stream = 3 km/h

19). Keshav can row 60 km downstream and 36 km upstream, taking 10 h each time. What is the velocity of the current?

A). 3 km/h

B). 2.2 km/h

C). 4 km/h

D). 1.2 km/h

View Answer

Correct Answer: 1.2 km/h

Speed downstream = \( \Large \frac{Distance}{Time} = \frac{60}{10} \) = 6 km/h

Speed upstream = \( \Large \frac{Distance}{Time} = \frac{36}{10} \) = 3.6 km/h

Therefore, Velocity of the current

= \( \Large \frac{1}{2} \) (Speed downstream - Speed upstream)

= \( \Large \frac{1}{2} \left(6-3.6\right) = \frac{2.4}{2} \) = 1.2 km/h

20). What time will be taken by a boat to cover a distance of 128 km along the stream, if speed of a boat in still water is 24 km/h and speed of stream is 8 km/h?

A). 8 hrs

B). 4 hrs

C). 7 hrs

D). 6 hrs

View Answer

Correct Answer: 4 hrs

Given,

Speed of boat in still water = x = 24 km/h

Speed of stream = y = 8 km/h

Therefore, Downstream speed of boat = x+y = 24+8 = 32km/h

Therefore, Required time = \( \Large \frac{Distance}{Speed (downstream)} \)

\( \Large \frac{128}{32} \) = 4 hrs

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