Multiple choice

A motor boat goes 10 km upstream and returns back to starting point in 55 minutes. The speed of motor boat in still water is 22 km/hr then speed of current is:

  1. $-2 km/hr$
  2. $2 km/hr$
  3. $4 km/hr$
  4. $3 km/hr$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Using time = distance/speed: Upstream speed = 22-c, downstream = 22+c. Total time = 10/(22-c) + 10/(22+c) = 55/60 hours. Solving gives c=2 km/hr. Negative current speed is physically impossible.

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