Multiple choice

A boatman can row 4 km against the stream in 20 minutes and return in 15 minutes. Find the rate of current?

  1. $3 km/hr$
  2. $2 km/hr$
  3. $2.5 km/hr$
  4. $1.5 km/hr$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Against stream: speed = 4 km / (20/60) hr = 12 kmph. With stream: speed = 4 km / (15/60) hr = 16 kmph. Let boat speed = b, current = c. Then b - c = 12 and b + c = 16. Solving: b = 14 kmph, c = 2 kmph. Rate of current is 2 km/hr. Option A (3 km/hr) and C (2.5 km/hr) don't satisfy both conditions.

Keep practicing — related questions