A circular road encloses a park. Madhu and Nandhan are participated in the street competition to go round the park. Madhu takes 28 minutes to complete one circuit of the sector, while Nandhan takes just 21 minutes. Assume they both begin at the same time and place and travel in the same direction. How long would take them to meet again at the starting point?
Madhu and Nandhan meet at the starting point after .