Multiple choice

The speed of current is 5 km./hr. A motorboat goes 10 km. upstream and back again to the starting point in 50 minutes. The speed in km./hr. of the motor boat in still water is -

  1. 20

  2. 26

  3. 25

  4. 28

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let boat speed in still water be x km/hr. Upstream speed = x-5, downstream speed = x+5. Time = distance/speed, so 10/(x-5) + 10/(x+5) = 50/60 hours. Solving gives x = 25 km/hr.