A speedboat tracks 42 km downstream in 2 hours and handles the same route upstream in 3 hours. Find the speed of the river stream. MCQ with Answer and Explanation

Question

A speedboat tracks 42 km downstream in 2 hours and handles the same route upstream in 3 hours. Find the speed of the river stream.

A. 4.5 km/h

B. 3.0 km/h

C. 4.0 km/h

D. 3.5 km/h

Answer: Option D

Solution (By JKSSB Mock Tests)

Downstream speed = 42 / 2 = 21 km/h. Upstream speed = 42 / 3 = 14 km/h. Speed of current = (Downstream speed - Upstream speed) / 2 = (21 - 14) / 2 = 7 / 2 = 3.5 km/h.

This question belongs to: Maths Time Speed and Distance

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Two trains 150 meters and 100 meters long are running along parallel tracks in the same direction at speeds of 56 km/h and 46 km/h respectively. In what time will the faster train cross the slower train completely?

A. 100 seconds

B. 80 seconds

C. 90 seconds

D. 110 seconds

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Correct Answer: Option C

Explanation:
Total distance = 150 + 100 = 250 meters. Relative speed in same direction = 56 - 46 = 10 km/h = 10 * (5/18) = 25/9 m/s. Time required = 250 / (25/9) = 250 * 9 / 25 = 90 seconds.

This question belongs to: Maths Time Speed and Distance