Page 130 - ICSE Math 4

Example 1: Find the perimeter of the following fi gures with the help of the given
measurements.

(a) A 5 cm B (b) P 3 cm Q

3 cm 3 cm 3 cm 3 cm

D C S R
5 cm 3 cm

Solu on: (a) Perimeter of rectangle ABCD = Sum of all the sides of rectangle ABCD

= AB + BC + CD + DA

= 5 cm + 3 cm + 5 cm + 3 cm = 16 cm

(b) Perimeter of square PQRS = Sum of all the sides of square PQRS

= PQ + QR + RS + SP
= 3 cm + 3 cm + 3 cm + 3 cm = 12 cm

Finding Perimeter Using a Square Grid

We know that a square grid is made of a number of unit squares. It can be used to fi nd
the perimeter of any closed fi gure. We can fi nd the perimeter of any plane closed fi gure
by drawing it on a square grid and then coun ng the number of unit lengths along the
boundary of the given fi gure.
1 cm
Look at the fi gure given alongside and let’s fi nd its perimeter. A B
Each square of the square grid is of 1 cm side. D C
E
Thus, perimeter of ABCDEFGH = AB + BC + CD + DE + EF + FG F
+ GH + HA H G

= 3 cm + 1 cm + 1 cm + 1 cm + 2 cm + 1 cm + 4 cm + 3 cm
= 16 cm

Mental Maths

Find the perimeter of the following shapes. Each side of the square in the square grid is
of 1 cm.

(a) (b) (c)

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