Question

Two bike riders ride around a circular path. The first rider completes one round in 12 minutes and the second rider complete it in 18 minutes. If they both start at the same place and the same time and go in the same direction, after how many minutes will they meet in the same place again?

Answer 1

Every 12 minutes, rider A reaches the start (that is, 12, 24, 36, ...)
Every 18 minutes, rider B reaches the start (that is, 18, 36, ...)

Then, rider B takes the same amount of time to finish 2 laps compared to rider A finishing 3 laps.
Thus, they will meet again after 36 minutes.