# 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
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
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
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
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