Multiple choice

A boat goes 60 km downstream in 6 hours to reach the destination. The boat will take total 21 hour if it has to go back to the starting point and come back to the destination. Find the speed of boat in still water? (in km/hr)

  1. 7

  2. 9

  3. 13

  4. 14

  5. Cannot be determined
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Downstream speed = 60/6 = 10 km/hr. If total round trip time is 21 hours and downstream takes 6 hours, upstream takes 15 hours, giving upstream speed = 60/15 = 4 km/hr. Solving u+v=10 and u-v=4 gives u=7 km/hr.

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