2
Q:

A man swims downstream 72 km and upstream 45 km taking 9 hours each time; what is the speed of the current  ?

A) 1 kmph B) 3.2 kmph
C) 1.5 kmph D) 2 kmph

Answer:   C) 1.5 kmph



Explanation:

72 --- 9
? ---- 1

=> Down Stream = 8

45 ---- 9 
? ---- 1

=> Up Stream = 5

Speed od current S = ?

S = (8 - 5)/2 = 1.5 kmph.

Q:

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 & Explanation Answer: A) 4 kmph

Explanation:

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

i.e,

d8 - C = 3 x d8 + C

 24 - 3C = 8 + C 4C = 16 C = 4 kmph

 

Hence, the speed of the current C = 4 kmph.

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3 36
Q:

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

A) 1 : 3 B) 3 : 2
C) 2 : 3 D) 3 : 1
 
Answer & Explanation Answer: A) 1 : 3

Explanation:

Let the speed of the boat in still water is 'w'

Speed of the current is 'c'

Let the distance between two places is 'd'

According to the question, motorboat takes half time to cover a certain distance downstream than upstream.

dw+c = 12dw-c

=> 2w - 2c = w + c

=> w = 3c

=> c : w = 1 : 3

 

Hence, the ratio between rate of current(c) and rate of boat in still water(w) = 1 : 3

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3 43
Q:

If sum of upstream and downstream speed of a boat is 82 kmph, and the boat travels 105 km. upstream in 3 hr, Find the time taken by boat to cover 126 km downstream. 

A) 2.8 hrs B) 2.7 hrs
C) 2.6 hrs D) 2.5 hrs
 
Answer & Explanation Answer: B) 2.7 hrs

Explanation:

Let Speed of boat in still water = b

Let Speed of still water = w

Then we know that,

Speed of Upstream = U = boat - water

Speed of Downstream = D = boat + water

Given, U + D = 82

b - w + b + w = 82

2b = 82

=> b = 41 kmph

From the given data,

41 - w = 105/3 = 35

w = 6 kmph

Now,

b + w = 126/t

=> 41 + 6 = 126/t

=> t = 126/47  = 2.68 hrs.

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4 43
Q:

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 & Explanation Answer: D) 8:3

Explanation:

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

 

Time for upstream = 8 hrs 48 min = 845hrs

 

Time for downstream = 4 hrs

 

Distance in both the cases is same.

 

=> p x  845= q x 4

 

=> 44p/5 = 4q

 

=> q = 11p/5

 

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

 

q+p2:q-p2

 

=> (11p/5 + p)/2  : (11p/5 - p)/2

 

=> 8 : 3

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7 291
Q:

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 & Explanation Answer: A) 9

Explanation:

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

= 1/2 (12 + 6) kmph = 9 kmph.

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7 138
Q:

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 & Explanation Answer: D) 8:3

Explanation:

Let the man's rate upstream be x kmph and that downstream be y kmph.

Then, distance covered upstream in 8 hrs 48 min = Distance covered downstream in 4 hrs.

x x 8 4 = (y x 4)
5
44 x =4y
5
 y = 11 x.
5
 Required ratio = y + x : y - x
2 2
   = 16x x 1 : 6x x 1
5 2 5 2
   = 8 : 3
5 5

   = 8 : 3.

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8 147
Q:

A man can row upstream at 16 km/hr and downstream at 24 km/hr. Find the speed of the current.

A) 4 kmph B) 6 kmph
C) 5 kmph D) 3 kmph
 
Answer & Explanation Answer: A) 4 kmph

Explanation:

Speed of the current = 24-16/2

= 8/2

= 4 km/hr.

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7 164
Q:

A motorboat can go 10 miles downstream on a river in 20 min. It takes 30 min for this boat to go back at the same 10 miles. Find the speed of the current ?

A) 8 m/h B) 5 m/h
C) 7 m/h D) 6 m/h
 
Answer & Explanation Answer: B) 5 m/h

Explanation:

As the distance travelled is constant, the time taken is inversely proportional to speed.

Let 'u' be the speed of the current and 'v' be the speed of the boat.

Speed of the boat downstream = v + u & upstream = v - u

=> v+u/v-u = 30/20 => v/u = 5 => v = 5u

=> v + u = 6u = 10/20/60 miles/hr

=> 6u = 30 m/h

=> u = 5 m/h

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