Multiple choice

A motorboat, whose speed in 20 km/hr in still water goes 90 km downstream in 4 hours. To come in same time what percentage of speed has to increase of motorboat?

  1. 25%

  2. 12.5%

  3. 20%

  4. 27.5%
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A Correct answer
Explanation

Downstream speed = 90/4 = 22.5 km/hr. If boat speed in still water is 20 km/hr, let stream speed be x. Then 20 + x = 22.5, so x = 2.5 km/hr. Upstream speed would be 20 - 2.5 = 17.5 km/hr. To cover 90 km upstream in 4 hours, speed needed = 90/4 = 22.5 km/hr. Increase from 17.5 to 22.5 = 5 km/hr. Percentage increase = (5/20) × 100 = 25%.

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