Amy and Chang walk around a track. Any walks each lap in 9 minutes. Chang walks each lap in 12 minutes. The two of them begin at the the starting line at the same time. They walk until they meet up again at the starting line. How many laps did Amy complete.

They meet up when Amy complete her fourth lap

Step-by-step explanation:

Amy walk around a track one lap in 9 minutes

Chang walk around a track one lap in 12 minutes

The relation between 9 and 12 will give the answer to this question

36 is a minimum common multiple, since

36/9 = 4

And

36 / 12 = 3

If Amy do the lap in 9 minutes, in 36 minutes she will do 4 laps

If Chang do the lap in 12 minutes, in 36 minutes will do 3 laps

Then They meet up again when Amy finished 4 laps