6
Q:

# A motor boat takes 12 hours to go downstream and it takes 24 hours to return  the same distance. what is the time taken by  boat in still water?

 A) 15 h B) 16 h C) 8 h D) 20 h

Explanation:

If t1 and t2 are the upstream and down stream times. Then time taken in still water is given by

$\frac{2×t1×t2}{t1+t2}=\frac{2×12×24}{36}=16h$

Q:

A man can row against the current three fourth of a kilometer in 15 min and returns same distance in 10 min, then ratio of his speed to that of current?

 A) 5:1 B) 3:1 C) 4:1 D) 2:1

Explanation:

Let the speed of the man in still water = p kmph

Speed of the current = s kmph

Now, according to the questions

(p + s) x 10 = (p - s) x 15

2p + 2s = 3p - 3s

=> p : s = 5 : 1

Hence, ratio of his speed to that of current = 5:1.

1 81
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

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,

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

3 92
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

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.

=> 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

3 84
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

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.

4 103
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

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 = $8\frac{4}{5}$hrs

Time for downstream = 4 hrs

Distance in both the cases is same.

=> p x  $8\frac{4}{5}$= q x 4

=> 44p/5 = 4q

=> q = 11p/5

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

$\frac{\mathbf{q}\mathbf{+}\mathbf{p}}{\mathbf{2}}\mathbf{:}\frac{\mathbf{q}\mathbf{-}\mathbf{p}}{\mathbf{2}}$

=> (11p/5 + p)/2  : (11p/5 - p)/2

=> 8 : 3

7 353
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

Explanation:

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

= 1/2 (12 + 6) kmph = 9 kmph.

7 551
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

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.

8 190
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