Question

If the radius of a circle is increased by $10\%$, then the corresponding area of new circle will be _______.

• A. $121\pi r^2$
• B. $12.1\pi r^2$
• C. $1.21\pi r^2$
• D. None of the given three

Answer 1

The correct option is C $1.21\pi r^2$

Let the original radius be $x$.

Then, new radius $=x+\frac{10}{100}x=1\cdot 1x$.

Therefore, area $=\pi r^2$

$=\pi (1\cdot 1x{)}^2$

$=1\cdot 21x^2)$

$=\pi (1\cdot 21\pi x^2$

$=1\cdot 21\pi r^2$.

Hence, option $C$ is correct.