Question

Use the identity $(a+b)(a-b)=a^2-b^2$ to evaluate:
$9.8\times 10.2$.

• A. $98.96$
• B. $99.86$
• C. $98.86$
• D. $99.96$

Answer 1

Answer: (D)

$99.96$

We know, $9.8\times 10.2=(10-0.2)\times (10+0.2)$ .
Applying the formula $(a+b)(a-b)=a^2-b^2$, where $a=10,b=0.2$,

we get,
$9.8\times 10.2=(10-0.2)\times (10+0.2)={10}^2-(0.2{)}^2=100-0.04=99.96.$

Therefore, option $D$ is correct.