A person row a boat 45 km downstream in 3 hours and manages the return journey upstream in 9 hours. Find the speed of the river current. MCQ with Answer and Explanation

Question

A person row a boat 45 km downstream in 3 hours and manages the return journey upstream in 9 hours. Find the speed of the river current.

A. 5.5 km/h

B. 5.0 km/h

C. 6.0 km/h

D. 4.5 km/h

Answer: Option B

Solution (By JKSSB Mock Tests)

Downstream speed = 45 / 3 = 15 km/h. Upstream speed = 45 / 9 = 5 km/h. Speed of current = (15 - 5) / 2 = 10 / 2 = 5 km/h.

This question belongs to: Maths Time Speed and Distance

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Question #1

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A train 120 meters long passes a signal pole in 6 seconds. Find the time it takes to completely cross a platform 240 meters long.

A. 22 seconds

B. 16 seconds

C. 18 seconds

D. 20 seconds

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Correct Answer: Option C

Explanation:
Speed of train = 120 / 6 = 20 m/s. Total distance to pass platform = 120 + 240 = 360 meters. Time required = 360 / 20 = 18 seconds.

This question belongs to: Maths Time Speed and Distance

Question #2

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In a 500-meter dash trial heat, runner A clocks across the tape in 50 seconds, while runner B marks a finish layout in 55 seconds. By what distance does runner A beat runner B?

A. 42.34 meters

B. 48.25 meters

C. 50.00 meters

D. 45.45 meters

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Correct Answer: Option D

Explanation:
Speed of runner B = 500 / 55 = 100 / 11 m/s. Distance covered by runner B when runner A finishes at 50 seconds = (100 / 11) * 50 = 5000 / 11 = 454.54 meters. Margin distance = 500 - 454.54 = 45.45 meters.

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Question #3

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A car covers a certain distance at 45 km/h. If it increases its speed to 60 km/h, it arrives 30 minutes earlier. Find the total distance.

A. 120 km

B. 90 km

C. 80 km

D. 100 km

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Correct Answer: Option B

Explanation:
Time difference = 30 minutes = 0.5 hours. Let distance be d. d / 45 - d / 60 = 0.5 => (4d - 3d) / 180 = 0.5 => d / 180 = 0.5 => d = 90 km.

This question belongs to: Maths Time Speed and Distance

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