Page 101 - Maths Skill - 6

Perimeter and Area 99

INTRODUCTION 6 cm
Aman and Udita bought two pieces of 11 cm
cloth from a shop. 5 cm
Their pieces looked like this (Fig. (a)) 3 cm
Both could not make out whose piece is bigger. Piece A Piece B

Can you suggest some ways to find out whose piece is bigger? Fig. (a)
In another situation, let’s imagine yourself going for morning walk around a square park. If you want to know how
much distance you have covered. How will you find it?
You must have seen the boundary wall of your school. This boundary is called perimeter. The perimeter of a figure
is the length of the boundary of a closed figure. Look at the figures given below.

(a) (b) (c) (d)
The boundaries of the figures constitute the perimeter. The perimeter can be measured in terms of mm, cm or m etc.

PERIMETER

The sum of the lengths of the line segments, enclosing a polygon is called its perimeter. Let’s
now learn how to calculate the perimeter of a closed figure.

Look at the adjoining Fig. As we know that, the sum of the length of all the sides of a figure is
its perimeter. So, the perimeter of figure is AB + BC + CD + DE + EA.

Unit of Perimeter
The perimeter of any closed figure is measured in mm, cm, m or km. To make it easier for you, here is the
conversion table.
1 Fact-o-meter
10 mm = 1 cm OR 1 mm = 10 cm � Perimeter can be found only for

1 closed figures. Perimeter of a
100 cm = 1 m OR 1 cm = 100 m circle is called its circumference.

1
1000 m = 1 km OR 1 m = 1000 km

PERIMETER OF A RECTANGLE
Let us recapitulate, what is a rectangle? P S

A rectangle PQRS is a polygon with four sides as shown in the figure. Its another
property is PQ = RS and PS = QR.

Now, let’s find its perimeter.
Perimeter of a rectangle PQRS = Sum of the lengths of its four sides. Q R
= PQ + QR + RS + PS

= PQ + QR + PQ + QR [ RS = PQ and PS = QR]
= 2 × PQ + 2 × QR = 2 × (PQ + QR)

Perimeter of rectangle = 2 × (length + breadth)