On a 1.2 km circular track, Rahul runs at 9 km/h and Sana at 15 km/h, starting together from the same point in opposite directions. After how many minutes do they first meet again at the starting point?

Explanation

1. 01

   Rahul's lap time $= \frac{1.2}{9}$ $h = 8$ min; Sana's $= \frac{1.2}{15}$ $h = 4.8$ min.

2. 02

   Both are back at the start together at a common multiple of 8 and 4.8 minutes.

3. 03

   Multiples of 8: 8, 16, 24 … ; $24 = 5 \times 4.8$. The first common one is 24 min.