A homeschool adventure

Something arrived
through the door…

Five mysterious letters have been delivered. Open each one to find out what's going on.

About this lesson

This is a story-driven maths lesson about perimeter. A series of urgent (and increasingly suspicious) letters arrive from TrustUs Corporation, each demanding that your children calculate the perimeter of a shape and buy the right amount of slug tape to protect their money box. The fifth letter reveals the whole thing was a scam — and recruits the children as crime-fighting agents.

How to run it

  1. Open the letters one at a time — don't reveal them all at once.
  2. After each letter, get out a ruler and measure the real money box (or draw the shape on paper with labelled sides).
  3. Fill in the order form together: calculate the perimeter, then multiply by the price per cm.
  4. Build suspense — act like you're worried about the slugs. The sillier, the better.
  5. Open letter 5 last, once the maths is done.

Learning outcomes

  • Understand perimeter as the total distance around the outside of a shape
  • Calculate the perimeter of a square (4 equal sides)
  • Calculate the perimeter of a rectangle (2 pairs of sides)
  • Calculate the perimeter of a triangle (add all three sides)
  • Apply perimeter to a real object and a practical problem
  • Multiply a length by a price to find a total cost
or tap each envelope to unseal it