a motorboat whose speed is 18 km/hr in still water - Wikitechy https://www.wikitechy.com/interview-questions/tag/a-motorboat-whose-speed-is-18-km-hr-in-still-water/ Interview Questions Mon, 06 Sep 2021 05:28:23 +0000 en-US hourly 1 https://wordpress.org/?v=6.9 https://www.wikitechy.com/interview-questions/wp-content/uploads/2025/10/cropped-wikitechy-icon-32x32.png a motorboat whose speed is 18 km/hr in still water - Wikitechy https://www.wikitechy.com/interview-questions/tag/a-motorboat-whose-speed-is-18-km-hr-in-still-water/ 32 32 A motorboat whose speed is 15 km/hr in still water goes 30km downstream and comes back in four and a half hours. The speed of the stream is ? https://www.wikitechy.com/interview-questions/boats-and-streams/a-motorboat-whose-speed-is-15-km-hr-in-still-water-goes-30km-downstream-and-comes-back-in-four-and-a-half-hours-the-speed-of-the-stream-is/ https://www.wikitechy.com/interview-questions/boats-and-streams/a-motorboat-whose-speed-is-15-km-hr-in-still-water-goes-30km-downstream-and-comes-back-in-four-and-a-half-hours-the-speed-of-the-stream-is/#respond Wed, 18 Aug 2021 02:39:49 +0000 https://www.wikitechy.com/interview-questions/?p=2075

A motorboat whose speed is 15 km/hr in still water goes 30km downstream and comes back in four and a half hours. The speed of the stream is ?

A. 4.5 km/hr

B. 6 km/hr

C. 7 km/hr

D. 5 km/hr

Answer : D. 5 km/hr

Explanation :

Let the speed of the stream be x km/hr. Then,
Speed downstream = (15 + x) km/hr
Speed upstream = (15 – x) km/hr

We know from question that it took 4(1/2)hrs to travel back to same point.
So, (30/15 + x) + (30/15 − x) = 4(1/2)
=> 900/225 − x2 = 9/2
=> 9x2 = 225
=> x = 5km/hr.

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