Worked example
A 12 cm by 8 cm rectangle has a 4 cm by 3 cm rectangular corner cut out. What area remains?
84 cm².
Find the outer area, 12 × 8 = 96 cm². Subtract the removed rectangle, 4 × 3 = 12 cm². The remaining shaded area is 96 − 12 = 84 cm².
Move from rectangle cutouts to curved composite figures
Begin with rectangle-based cutouts: find the outer rectangle and subtract the removed rectangle. These are two-dimensional shaded-area questions, with answers in square units.
For a circular example, a capsule with a 24 cm by 16 cm rectangle and two radius-8 cm semicircular ends has area 24 × 16 + pi × 8². The semicircles make one circle, so the exact total is 384 + 64pi cm², or 585.1 cm² to the nearest tenth. Keep pi until the final rounding step.