If the radius of a circle is increased by 10%, what is the percentage increase in its area?

Correct option is B

Given
Initial radius increase = 10%

Formula Used
Percentage increase in Area = $$x + y + \frac{xy}{100}$$​​
Where x and y are the percentage changes in dimensions.

Solution
Since the area of a circle depends on the square of the radius (Area $$= \pi r^2$$​), the increase in radius happens in two dimensions.
Here, x = 10 and y = 10.
Percentage increase in Area = $$10 + 10 + \frac{10 \times 10}{100}$$​​
Percentage increase in Area = $$20 + \frac{100}{100}$$​​
Percentage increase in Area = 20 + 1 = 21%
Final Answer
So the correct answer is (b)