Two ribbons of $18 \mathrm{m}$ and $24 \mathrm{m}$ lengths are to be cut into smaller pieces of equal length. What will be the maximum length of each piece in metres?

Which of the following number is not divisible by $9$?

If two numbers are divisible by a number, then their$\_\_\_\_\_\_\_\_$is also divisible by that number.

The $\mathrm{HCF}$ of two co-prime or prime numbers is equal to _____