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Aptitude - Boats and Streams

Exercise : Boats and Streams - General Questions
1.
A boat can travel with a speed of 13 km/hr in still water. If the speed of the stream is 4 km/hr, find the time taken by the boat to go 68 km downstream.
2 hours
3 hours
4 hours
5 hours
Answer: Option
Explanation:

Speed downstream = (13 + 4) km/hr = 17 km/hr.

Time taken to travel 68 km downstream = 68 hrs = 4 hrs.
17

2.
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:
8.5 km/hr
9 km/hr
10 km/hr
12.5 km/hr
Answer: Option
Explanation:

Man's rate in still water = (15 - 2.5) km/hr = 12.5 km/hr.

Man's rate against the current = (12.5 - 2.5) km/hr = 10 km/hr.

3.
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?
2 : 1
3 : 2
8 : 3
Cannot be determined
None of these
Answer: Option
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.

4.
A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:
4
5
6
10
Answer: Option
Explanation:

Let the speed of the stream be x km/hr. Then,

Speed downstream = (15 + x) km/hr,

Speed upstream = (15 - x) km/hr.

30 + 30 = 4 1
(15 + x) (15 - x) 2

900 = 9
225 - x2 2

9x2 = 225

x2 = 25

x = 5 km/hr.

Video Explanation: https://youtu.be/lMFnNB3YQOo

5.
In one hour, a boat goes 11 km/hr along the stream and 5 km/hr against the stream. The speed of the boat in still water (in km/hr) is:
3 km/hr
5 km/hr
8 km/hr
9 km/hr
Answer: Option
Explanation:

Speed in still water = 1 (11 + 5) kmph = 8 kmph.
2

Video Explanation: https://youtu.be/KQX_mA3tcVA

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