If the sides of a square be double find the increase of percentage in area :

$$\eqalign{ & {A_1} = {x^2}{\text{ and }}{A_2} = {\left( {2x} \right)^2} = 4{x^2} \cr & {\text{Increase in area}} = \left( {4{x^2} - {x^2}} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 3{x^2} \cr & {\text{Increase % }} = \left( {\frac{{3{x^2}}}{{{x^2}}} \times 100} \right)\% \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 300\% \cr} $$