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 & Explanation
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 & Explanation
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 & Explanation
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 & Explanation
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
9×2 = 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 & Explanation
Answer: Option C
Explanation:
Speed in still water = 1 (11 + 5) kmph = 8 kmph.