Percentage

$A_{1} = \pi r^{2}$

$r + 0.2r = 1.2r$

$A_2 = \pi (1.2r)^{2}=\pi 1.44r^{2}$

The increase is $\boxed{44}$ % because $\Delta=A_2 - A_1 = 0.44$ and $0.44$ is the same as $44$ %.

Area of circle is pi X radius squarem Considering 100 cm as radius it is 120 cm now so increase in area is 4400 that is 44% ans K.K.GARG,India

The scale factor for the enlargement is 1.2. To find the new area, multiply the original area by the square of the scale factor. 1.2 x 1.2 = 1.44. The area has increased by 0.44 of its original area. This equates to a 44% increase.

I thought about a circle with radius 10 and compared it to a circle with radius 12 (20% longer than the first radius) I calculated the 10 % of the first circle and counted how many times it was contained in the second circle. It resulted to be 14.4 times. That means the second circle has grown 10% by 4.4 times = 44%

r1=r+20%r r1=1.2r area=pi. r1^2 area=pi. (1.2r)^2 Area=1.44(pi. r^2) Area= 44% {area} As area of circle =pi. r^2