Question : If the radius of a circle is increased by 10%, what will be the percentage increase in the area of the circle?
Option 1: 19
Option 2: 20
Option 3: 21
Option 4: 23
Correct Answer: 21
Solution : Let the radius of the original circle = $r$ So, the area of the original circle = $\pi r^2$ Radius of circle after 10% increase = $r+\frac{10r}{100} =1.1r$ Area of new circle = $\pi \times 1.1^2 = 1.21r^2$ Percentage increase in area = $\frac{1.21\pi r^2- \pi r^2}{\pi ^2}\times 100$ = 21% Hence, the correct answer is 21.
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