If  each side of a cube is doubled , then the percentage change in the surface area is:

300%

Surface area of cube = 6a²

After doubling each side of the cube

new surface area = 6 (2a)²

                            = 4 (6a²)

                            = 4 (actual surface area)

Surface area ⇒ Old : New = 1 :  4

Increased percentage = \(\frac{3}{1}\) × 100 = 300%