Multiple choice

A boat takes 6 hrs to travel 144 km downstream. The speed of the boat downstream is 1.5 times of the speed of the boat upstream. What is the speed of the current (in kmph)?

  1. 4 km / hrs

  2. 20 km / hrs

  3. 6 km / hrs

  4. 18 km / hrs

  5. None of these

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

Downstream speed is distance/time = 144/6 = 24 kmph. Since downstream speed is 1.5 × upstream speed, upstream speed = 24/1.5 = 16 kmph. Current speed is half the difference between downstream and upstream: (24-16)/2 = 4 kmph. Current always adds to downstream and subtracts from upstream.