Area & perimeter

For a rectangle, area = length × width and perimeter = 2 × (length + width). A 5 cm by 3 cm rectangle has area 15 cm² and perimeter 2 × (5 + 3) = 16 cm. A square is just a rectangle with equal sides, so a 7 cm square has area 7 × 7 = 49 cm².

A triangle's area is half of the rectangle that would box it in: area = ½ × base × height. With base 8 cm and height 5 cm, that is ½ × 40 = 20 cm². The perimeter is simply the three side lengths added together.

Trickier shapes are made of simple ones. Split an L-shape into two rectangles, find each area, and add them. If a corner is cut out of a rectangle, find the whole area and subtract the missing piece. A 10 × 8 rectangle (80 cm²) with a 4 × 3 corner removed (12 cm²) leaves 68 cm².

Length is measured in units like cm; area is in square units (cm²) because it covers a surface. Keep the unit in mind, but for these puzzles just type the number — the unit is already stated for you.