LCM and HCF Practice Test 1

A, B and C will take 4 hours, $\frac{12}{7}$ hours and $\frac{12}{13}$ hours respectively in completing one round on the circular path.
∴ LCM of $\frac{4}{1},\frac{12}{7}$ and $\frac{12}{13}$ $=\frac{\mathrm{LCM}\mathrm{of}4,12\mathrm{and}12}{\mathrm{HCF}\mathrm{of}1,7\mathrm{and}13}$
∵ LCM of 4, 12 and 12= 12 and HCF of 1, 7 and 13 = 1
∴ Required LCM $=\frac{12}{1}=12$
Hence, they will meet together again after 12 hrs.