Two race cars are speeding around the racetrack at different speeds. One goes around the track in 2 minutes; the other goes around the track in 11/2 minutes. How often does the faster car pass the slower car?

The least common multiple of 1 1/2 and 2 is
LCM[1 1/2, 2] = LCM[3/2, 2] = LCM[3/2, 4/2] = (1/2)LCM[3, 4] = (1/2)(12) = 6
In 6 minutes, the faster car will have made 4 laps and the slower car will have made 3 laps.

The faster car will lap the slower one every 6 minutes.

58