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Perimeter (practice)
Textbook Part 4, pp. 16–17
GoalFind the perimeter of regular polygons and composite shapes; write it with the letter P.
New words
the letter P (perimeter) · P harfiribbon / tape · tasmagrid square · katak
Explanation
Perimeter is written with the letter P. For a regular polygon you only need to measure one side, then add it as many times as there are sides: a regular triangle with 3 cm sides: P = 3 + 3 + 3 = 9 cm.
Worked examples
A regular pentagon with 2 cm sides: P = 2 + 2 + 2 + 2 + 2 = 10 cm.
Edging a table with ribbon: sides 30, 15, 30, 15 cm → 30 + 15 + 30 + 15 = 90 cm.
Class activity
On squared paper (2 squares = 1 cm) children draw different polygons and find the perimeter by counting squares.
Practice
1
Regular triangle, side 7 cm. P = ?
21 cm
2
Regular hexagon, side 3 cm. P = ?
18 cm
3
A table’s sides are 30, 15, 30, 15 cm. Length of ribbon needed?
90 cm
4
Write the answers in decreasing order: 30 + 25, 70 − 10, 44 + 4
60, 55, 48