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QA – Placement Quizzes | Trains, Boats and Streams | Question 2

  • Difficulty Level : Hard
  • Last Updated : 28 Jun, 2021

A speedboat runs 6 km upstream in a river and comes back to the starting point in 33 minutes. The stream of the river is running at 2 km/hr. What is the speed of speedboat in still water?
(A) 25 km/h
(B) 21 km/h
(C) 26 km/h
(D) 22 km/h


Answer: (D)

Explanation: Let the speed of speedboat in still water be x km/h.
Then, speed downstream = (x + 2) km/h, speed upstream = (x – 2) km/h.
Since it goes 6 km upstream and comes back in 33 minutes, we have
6/(x+2) + 6/(x-2) = 33/60
⇒ 11x² – 240x – 44 = 0
⇒ 11x² – 242x + 2x – 44 = 0
⇒ (x – 22)(11x + 2) = 0
⇒ x = 22.
Therefore, the required speed = 22 km/h.

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