Anjali and Deepa start together from the same point of a circular track 900 m round and run in the same direction at 9 km/h and 6 km/h. Anjali first overtakes Deepa after how many minutes?

In the same direction the gap opens at the difference of the speeds, 9 − 6 = 3 km/h = 3000/60 = 50 m per minute. To overtake, Anjali must gain a whole lap of 900 m, which takes 900/50 = 18 minutes. (Adding the speeds — right only for opposite directions — gives 15 km/h = 250 m/min and the trap 3.6 minutes.)