Answer:
After 315 minutes both person will be together
Explanation:
We have given that first person takes 21 minutes to complete the one round and second person takes 45 minutes to complete the one round
We have to find the time at which both person will be together
That time will be equal to LCM of both time
That is LCM of 21 and 45
Factor of 21 = 3×7
Factor of 45 = 3×3×5
So LCM will be 3×3×5×7=315 minutes
So after 315 minutes both person will be together