1.1. (4 points) Find the least common multiple of the numbers 28 and 72.
Answer: 504.

Solution. We have $28=2^{2} \cdot 7, 72=2^{3} \cdot 3^{2}$, therefore $\operatorname{LCM}(28,72)=2^{3} \cdot 3^{2} \cdot 7=504$.