Question

If the radius of a circle is increased by 100%, then the area is increased by:

(A)100% (B) 200% (C) 300% (D) 400% (E) none of these

Answer 1

hope this helps in the picture below :)

Answer 2

`A_1=\pi r^2\\\\R=2r\ then\ A_2=\pi R^2\to A_2=\pi(2r)^2=4\pi r^2\\\\A_2-A_1=4\pi r^2-\pi r^2=3\pi r^2=3A_1\\\\3=300\%\\\\Answer:(C).`