# Boats and Streams – Aptitude test, questions, shortcuts

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.
 A. 2 hours B. 3 hours C. 4 hours D. 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:
 A. 8.5 km/hr B. 9 km/hr C. 10 km/hr D. 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?
 A. 2 : 1 B. 3 : 2 C. 8 : 3 D. Cannot be determined E. 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:
 A. 4 B. 5 C. 6 D. 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.

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:
 A. 3 km/hr B. 5 km/hr C. 8 km/hr D. 9 km/hr