A man can row 12 km/h in still water. He finds that it takes him twice as long to row upstream as to row downstream. Find the speed of the stream. MCQ with Answer and Explanation

A man can row 12 km/h in still water. He finds that it takes him twice as long to row upstream as to row downstream. Find the speed of the stream.
A. 4 km/h
B. 3 km/h
C. 5 km/h
D. 6 km/h
Answer: Option A
Solution (By JKSSB Mock Tests)
Let stream speed be c. Upstream speed = 12 - c, Downstream speed = 12 + c. Given: 2 * (12 - c) = 12 + c => 24 - 2c = 12 + c => 3c = 12 => c = 4 km/h.

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Practice More Time Speed and Distance Questions

Question #1
Excluding operational station stops, a city bus routes at an average of 42 km/h, and including stops its net average speed is 35 km/h. For how many minutes does it stop per hour?
A. 12 minutes
B. 10 minutes
C. 14 minutes
D. 8 minutes

Correct Answer: Option B


Explanation:
Stoppage time per hour = (42 - 35) / 42 = 7 / 42 = 1/6 hour = 10 minutes.

This question belongs to: Maths Time Speed and Distance
Question #2
A person row a boat 12 km downstream in 1 hour. If the river current flows at 3 km/h, find the time taken by the boat to row the same distance upstream.
A. 3.0 hours
B. 1.5 hours
C. 2.0 hours
D. 2.5 hours

Correct Answer: Option C


Explanation:
Downstream speed = 12 / 1 = 12 km/h. Baseline boat speed in still water = Downstream speed - Current speed = 12 - 3 = 9 km/h. Upstream speed = Still water speed - Current speed = 9 - 3 = 6 km/h. Time taken upstream = Distance / Upstream speed = 12 / 6 = 2 hours.

This question belongs to: Maths Time Speed and Distance
Question #3
A locomotive running at 54 km/h takes 20 seconds to completely cross a platform. If it takes 8 seconds to pass a standing point observer, find the platform length.
A. 160 meters
B. 220 meters
C. 200 meters
D. 180 meters

Correct Answer: Option D


Explanation:
Speed of train = 54 * (5/18) = 15 m/s. Length of train = Speed * Time to cross observer = 15 * 8 = 120 meters. Total distance to cross platform = Speed * Time = 15 * 20 = 300 meters. Platform length = 300 - 120 = 180 meters.

This question belongs to: Maths Time Speed and Distance