There is a circular path around a sports field. Sonia takes 18 minutes to drive one round of the field, while Ravi takes 12 minutes for the same. Suppose they both start at the same point and at the same time, and go in the same direction. After how many minutes will they meet again at the starting point?

Sonia and Ravi start from the same point, at the same time and in the same direction. So they meet again after the least common multiple (LCM) of the times taken by them individually. To get the LCM we have to factorize the numbers.
Factors of 18 = 2 × 3 × 3
Factors of 12 = 2 × 2 × 3
LCM = 2 × 2 × 3 × 3 = 36
Hence, they will meet together at the starting point after 36 minutes.