Multiple choice

A person noticed that when the water is still, his boat can go at a speed of 16 km/hr. It takes 200% more time to go against the flow the water than going along with the flow for same distance. Find the difference between the speeds of water and boat in still water.

  1. 4 km/hr

  2. 5 km/hr

  3. 6 km/hr

  4. 8 km/hr

  5. 10 km/hr
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let boat speed = 16, water speed = w. Downstream = 16+w, Upstream = 16-w. Time = Distance/Speed. 200% more time means 3 times the time. 1/(16-w) = 3 * 1/(16+w). 16+w = 48-3w. 4w = 32. w = 8. Difference = 16 - 8 = 8.

AI explanation

A time difference of 200% means the upstream time is 3 times the downstream time for the same distance, making the downstream speed 3 times the upstream speed. Using the still water speed of 16 km/hr, the upstream speed is 0.5 times the speed of the stream subtracted from 16, and the downstream speed is 16 plus that same half; setting them in a 1 to 3 proportion yields 16 minus the stream speed equals 48 plus 3 times the stream speed. Solving gives the stream speed as 8 km/hr, and since the question asks for the difference between the speeds of the boat in still water and the stream, the result is 8 km/hr.

Keep practicing — related questions