Multiple choice general knowledge math & puzzles

A man can row 4.5 km/hr in still water. It takes him twice as long to row upstream as to row downstream. What is the rate of the current?

  1. 1.5 km/hr

  2. 2 km/hr

  3. 2.5 km/hr

  4. 1 km/hr

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

Let the current be c. Upstream speed = 4.5 - c, downstream = 4.5 + c. Rowing upstream takes twice as long, so 1/(4.5-c) = 2/(4.5+c). Solving gives 4.5 + c = 9 - 2c, so 3c = 4.5 and c = 1.5 km/hr, matching option A.