Multiple choice

A man can row 36 km downstream and return in a total of 5 hours. If the speed of the boat in still water is five times the speed of the current, then the speed of the current is

  1. 5 km/hr

  2. 8 km/hr

  3. 3 km/hr

  4. 6 km/hr

  5. None of these

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

Let current speed be c. Boat speed b = 5c. Downstream = 6c, Upstream = 4c. Time = 36/(6c) + 36/(4c) = 5. 6/c + 9/c = 5. 15/c = 5. c = 3.

AI explanation

Let the speed of the current be x km/hr, making the speed of the boat in still water 5x km/hr. The downstream speed is 6x km/hr and the upstream speed is 4x km/hr. Using the total time formula of distance divided by speed, 36 divided by 6x plus 36 divided by 4x equals 5. Solving this gives 6 divided by x plus 9 divided by x equals 5, so 15 divided by x equals 5 and x equals 3. The speed of the current is 3 km/hr.