A square of side 0.524375 cm is drawn on a square paper of side 2.524375 cm. Find the area of the paper not covered by the drawing, correct to 3 significant figures.
Worked solution (try it first)
The uncovered area is the big square minus the small one: 2.5243752−0.5243752.
Use the difference of two squares, a2−b2=(a−b)(a+b): this is 2×3.04875=6.0975 cm2.
To 3 significant figures, the fourth figure is 7, so round up: 6.10 cm2, option B.