📐 Regular Shapes 📚 Grade 3-4 ⏱ 5 min
Fast Perimeter for Regular Polygons
When all sides of a shape are equal, adding them one by one is not necessary. There is a faster way through multiplication.
Equal sides — multiplication instead of addition
A regular pentagon with a 6 cm side. Instead of 6+6+6+6+6, calculate 6×5=30 cm. Multiplication is just fast addition of equal numbers.
💡 Anchor: show it with a square, where the child already knows the formula P=a×4 — the same principle works for any number of equal sides.
Practice
A regular hexagon with a 4 cm side. Perimeter? 4×6=24 cm.
FAQ
Does this work for shapes with unequal sides?
No, only for regular shapes where all sides match — otherwise they must be added separately.