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.

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.