The product of two conjugate binomial surds is ...........

Use Euclid's division algorithm to find the $HCF$ of $441, 567, 693$.

$2.031 \overline{2}$ is ............

Simplify: $\frac{2}{\sqrt{5}-\sqrt{3}} + \frac{4}{\sqrt{10+\sqrt{84}}} - \frac{2}{\sqrt{7}-\sqrt{5}}$

Three sets of English,Hindi,and Mathematics books have to be stacked in such a way that all the books are stored topic-wise and the height of each stack is the same. The number of English books is $96$,the number of Hindi books is $240$,and the number of Mathematics books is $336$. Assuming that the books are of the same thickness,determine the number of stacks of English,Hindi,and Mathematics books.

Four bells toll at intervals of $8$,$12$,$15$,and $18$ seconds respectively. All four begin to toll together. How many times will they toll together in one hour,excluding the one at the start?