Grade 10 — Mathematics 10C › C10U01 Measurement Systems & Conversions

Grade 10 › C10U01 Measurement Systems & Conversions › L4
GRADE 10 · ALBERTAOUTCOME AB-MAT10C-M1

L4 · Perimeter Problems in Both Systems

Learning goal

“I can find the perimeter of rectangles, squares, triangles, and regular polygons in SI or imperial units, work backwards from a perimeter to a missing side, and handle problems where the sides are given in mixed units by converting first.”

Perimeter — the distance around a 2-D shape: the sum of all its side lengths, measured in a length unit (never a squared unit).
Regular polygon — all sides equal, all angles equal; perimeter = (number of sides) x (side length).
Composite perimeter problem — a real task (fencing, framing, edging) whose answer is a perimeter with an adjustment, e.g., leaving a gap for a gate.
Worked example

Perimeter of a rectangle 12 cm by 7 cm. Add all four sides, or double the two different sides: P = 2(12 + 7) = 2 x 19 = 38 cm. Backwards version: a rectangle has perimeter 40 cm and length 13 cm. The two lengths use 26 cm, leaving 40 - 26 = 14 cm for the two widths, so the width is 14 / 2 = 7 cm. Say it plainly: backwards perimeter problems are just the forwards addition with one piece unknown - undo it step by step.

Check yourself — explain it

In the backwards problem, why do we divide by 2 at the end?

Paired problem — example still visible

Perimeter of a square with side 9.5 m -> 38 m (4 x 9.5)

Faded completion — last step is yours

"Triangle sides 5 in, 7 in, 9 in: P = 5 + 7 + 9 = ___ in" -> 21 in

Ready to practise?

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

Start practice →Take the unit quiz