L1 · Perimeter of Rectangles

Learning goal

“I can find the perimeter of any rectangle - the distance all the way around it - by adding its four sides or by doubling the sum of its length and width, and I can find a missing side when I know the perimeter.”

Perimeter — the distance around the outside of a shape, measured in length units (cm, m, km). It is a walk around the edge, not a covering.

Length and width — the two different side lengths of a rectangle. Opposite sides of a rectangle are equal, so the four sides are length, width, length, width.

Side — one straight edge of the rectangle. A rectangle has 4 sides.

Worked example

A rectangular garden is 8 m long and 5 m wide. Step 1: Perimeter is a walk around the edge. Start at a corner and go all the way around: 8 m (long side), 5 m (short side), 8 m (the other long side), 5 m (the other short side). Step 2: Add them: 8 + 5 + 8 + 5 = 26. Perimeter = 26 m. Step 3: Notice the units: metres, NOT square metres. Perimeter is a length - a distance - so it takes a length unit. Say it plainly: opposite sides of a rectangle are equal, so every rectangle's perimeter is two lengths plus two widths. Forget one side and the walk never gets home.

Check yourself — explain it

A rectangle is 10 cm by 4 cm. Its perimeter is found by...

Paired problem — example still visible

A rectangle is 9 m by 6 m. Walk it: 9 + 6 + 9 + 6 = 30 m

Faded completion — last step is yours

"A rectangle is 12 cm by 3 cm: P = 12 + 3 + 12 + ___ = ___ cm" -> 3; 30 cm

Ready to practise?

10 scored questions with a 3-rung hint ladder. Mastery needs 8/10 plus both gate questions.

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