Perimeter

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Measurement Units

Perimeter: The distance around the figure. To find the perimeter, you just add the lengths of the sides.
The units of perimeter are mm, cm, m, km

Circumference:A special name given to the perimeter of a circle. It is measured as:

The units of circumference are mm, cm, m, km.

Example

1. Let's find the perimeter of this figure.

Perimeter of this shape is the total length around the figure.

Perimeter of figure (a)      = 7 × 4 - 3
                                        = 28 - 3
                                        = 25

Perimeter of figure (b) = 3 × 3 (There is only three sides to fig.(b) )
= 9

Perimeter of the shape      = Perimeter of (a) + Perimeter of (b)
                                        =            25            +         9
                                        =      34units

2. Let's find the perimeter of this semicircular pond.

The diameter of the pond is 7.2m. Therefore the radius of the circle is 7.2÷2=3.6m

The circumference of a circle, c = × d
The diameter of the circle is twice the radius. d = 2 × 3.6 = 7.2m

                                               c = × d
                                               c = × 7.2
Let's take = 3.142,               c = 3.142 × 7.2m
                                                  = 22.62 m
So, the length of semicircular arc is half the circumference.
That is 22.62m ÷ 2 = 11.31 m = 11.3 m ( rounded to one decimal place. )
The perimeter of the semicircular pond is :
the length of the semicircular arc + the diameter of the circle
11.3 + 7.2 = 18.5 m

Have a Go

Problem 1
Find the perimeter of this figure.

Practice Questions

Question 1
Find the perimeter of this shape.

Question 2
Find the perimeter of this flower bed.

Solution

This figure is made up of two shapes, a rectangle and a semicircle

Perimeter of Fig. (a)    = 12 + 6 + 12 = 30

Perimeter of Fig. (b)    = ½ × d       = 0.5 × 3.142 × 6
                                                           = 9.426m
                                                           = 9.4m (rounded off to 1decimal place)

Perimeter of the figure = Perimeter of Fig.(a) + Perimeter of Fig.(b)
                                  = 30 + 9.4
                                  = 39.4 m

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