Question

Evaluate $8.5\times 9.5$ using suitable standard identity.

Answer 1

As we know formula $(a+b)(a-b)$ = $a^2-b^2$
Writing $8.5$ as $9-0.5$ and $9.5$ as $9+0.5$
$\Rightarrow$ $(9+0.5)(9-0.5)$ = $9^2-(0.5{)}^2$ $=$ $81-0.25$
Hence the answer is $80.75$