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Boats & Streams

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51.

If a boat is rowed downstream for 50 km in 5 hours and upstream for 24 km in 6 hours, what is the speed of the boat and the river?

Answer: A

If x: speed of boats man in still water

y: speed of the river

Downstream speed (Ds) = x + y

Upstream speed (Us) = x – y

x = (Ds + Us) / 2

y = (Ds – Us) / 2,/p>

In the above problem Ds = 10 ; Us = 4

x = (10 + 4) / 2 = 14/2 = 7 km/hr

y = (10 - 4)/2 = 6/2 = 3 km/hr

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52.

A boat covers a distance of 30 km in 2 ½ hours running downstream while returning it covers the same distance in 3 ¾ hours. What is the speed of the boat in still water?

Answer: D

Speed downstream = (30 x 2/5)km/hr = 12km/hr 

 

Speed upstream = (30 x 4/15) km/hr = 8 km/hr 

 

Speed of boat in still water = ½ (12 + 8)km/hr = 10 km/hr

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53.

A man can row 6 kmph in still water. When the river is running at 1.2 kmph, it takes him 1 hour to row to a place and black. What is the total distance traveled by the man?

Answer: C

M = 6

S = 1.2

DS = 7.2

US = 4.8

x/7.2 + x/4.8 = 1

x = 2.88

 

D = 2.88 * 2 = 5.76

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54.

In a river, a man takes 3 hours in rowing 3 km upstream or 15 km downstream. What is the speed of the current?

Answer: A

Speed upstream = 3/3 km/hr =1 km/hr 

 

Speed downstream = 15/3 km/hr = 5 km/hr 

 

Speed of current = ½(5 -1) km/hr = 2 km/hr

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55.

Sahil can row 3 km against the stream in 20 minutes and he can return in 18 minutes. What is rate of current ?

Answer: A

No answer description available for this question.

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56.

A boats man can row in still water at speed of 7 km/hr. It takes 6 hours more to travel the same distance in upstream than in downstream if the speed of the river is 3 km/hr. what is the distance between the two destinations?

Answer: A

x = 7 km/hr ; y = 3 km/hr

Ds = 10 km/hr ; Us = 4 km/hr

Distance (d) is same. Therefore, if time taken for downstream is t hours, the time for upstream is (t + 6) hours.

10 × t = 4 × (t + 6)

6t = 24 ; t = 4 hours

d = 10 × 4 = 40 km

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57.

Michel can swim in still water at the rate of 6km per hour. After swimming in a stream, she realized that she takes twice the time to go upstream as she takes to go downstream. What is speed of the current?

Answer: B

No answer description available for this question.

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58.

A man can row three-quarters of a kilometer against the stream in 11 ¼ minutes and return in 7 ½ minutes. The speed of the man in still water is?

Answer: D

Distance covered upstream in 45/4min =3/4 km 

 

Distance covered upstream in 1 hr =(3/4 × 2/15 × 60) km/hr = 4 km/hr 

 

Distance covered downstream in 15/2 min = ¾ km 

 

Distance covered downstream in 1hr 

 

= (3/4 × 2/15 × 60)km/hr = 6 km/hr 

 

Speed of the man in still water 

 

= ½ (6 + 4)km/hr = 5 km/hr

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59.

The current of a stream at 1 kmph. A motor boat goes 35 km upstream and back to the starting point in 12 hours. The speed of the motor boat in still water is?

Answer: A

S = 1

M = x

DS = x + 1

US = x - 1

35/(x + 1) + 35/(x - 1) = 12

 

x = 6

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60.

A man can row with a speed of 15 kmph in still water. If the stream flows at 5 kmph, then the speed in downstream is?

Answer: C

No answer description available for this question.

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