smc

Increasing by $100\%$ is the same as doubling the radius. If we let $r$ be the radius of the old circle, then the radius of the new circle is $2r.$ Since the area of the circle is given by the formula $\pi r^2,$ the area of the new circle is $\pi (2r{)}^2=4\pi r^2.$ The area is quadrupled, or increased by $\boxed{300\%}$