shouldn't Numbers divisible by $5 = \left \lfloor {\frac{720}{5}} \right \rfloor = 144$, not that it affects the final result as $720$ is a multiple of $5$ itself.

However, in situations where it isn't multiple, e.g. we try to find no. of positive integers ($\leq 10$) divisible by $3$, we use $\left \lfloor {\frac{10}{3}} \right \rfloor = 3$, which is correct as the positive integers ($\leq 10$) divisible by $3$ are $3$, $6$ and $9$.