Boats and Streams – Aptitude test, questions, shortcuts

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

Answer: Option C

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

Answer: Option C

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

Answer: Option C

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

Answer: Option B

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

Answer: Option C

Explanation:

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

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