Question

The H.C.F of 45 and 81 is .

• A. 5
• B. 3
• C. 9

Answer 1

The correct option is C 9

Using prime factorisation method:

$\begin{array}{cc}3& 45\\ 3& 15\\ 5& 5\\ & 1\end{array}$

$\therefore 45=3\times 3\times 5$

$\begin{array}{cc}3& 81\\ 3& 27\\ 3& 9\\ 3& 3\\ & 1\end{array}$

$\therefore 81=3\times 3\times 3\times 3$

$45=5\times 3\times 3$
$81=3\times 3\times 3\times 3$

$\therefore$ The HCF is $3\times 3=9$