# QA – Placement Quizzes | Trains, Boats and Streams | Question 5

A motorboat crosses a certain distance in 1 hour and comes back in 1½ hours. If the stream is running at 3 km/h, find out the speed of motorboat in still water.**(A)** 10 km/h**(B)** 15 km/h**(C)** 12 km/h**(D)** None of these**Answer:** **(B)****Explanation:** Let the speed of motorboat in still water be x km/h. Then,

Downstream speed = (x + 3) km/h.

Upstream speed = (x – 3) km/h.

Then, (x + 3) × 1 = (x – 3) × 3/2

⇒ 2x + 6 = 3x – 9

⇒ x = 15.

So, the speed of motorboat in still water is 15 km/h.

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