4
Review: perimeter and broken line
Textbook: Part 1, lesson 4, pp. 10–11
GoalReview perimeter and the length of a broken line; comparing expressions without calculating.
New words
perimeter · perimetrside · tomonbroken line · siniq chiziqbrackets · qavs
Explanation
The perimeter is the sum of the lengths of all sides. The length of a broken line is the sum of its parts. Sometimes we can compare expressions without calculating: if most terms are the same, it is enough to compare the terms that differ.
Worked examples
A rectangle with sides 4 dm and 6 dm: P = 4 + 6 + 4 + 6 = 20 dm.
20 + 30 + 40 and 20 + 30 + 4: two terms are the same and 40 > 4, so the left side is bigger.
Class activity
“Wire fence”: each pair gets a piece of string. They measure the perimeter of a notebook or a book and say how much string is needed.
Practice
1
Perimeter of a rectangle with sides 4 dm and 6 dm (in dm)?
20
2
Perimeter of a square with side 4 cm (in cm)?
16
3
20 + 30 + 40 □ 20 + 30 + 4 (>, <, =)
>
4
Grandfather has 19 animals; 14 are sheep and the rest are goats. How many goats?
5