Page 149 - ICSE Math 5

Example 4: Find the perimeter of a square whose sides measure 6 cm each.
6 cm
Solution: Side of the given square = 6 cm
Perimeter of the square = 4 × Side
6 cm 6 cm
= 4 × 6 cm = 24 cm
So, the perimeter of the given square is 24 cm.
6 cm
Example 5: Find the measure of each side of a square whose perimeter is 48 cm.
Solution: Perimeter of the given square = 48 cm
Perimeter
 Side of the given square =
4
48
= cm = 12 cm
4
So, the length of each side of the given square is 12 cm.

Perimeter of a Triangle

We know that a triangle is a simple closed figure having 3 sides. L
Let’s find the formula to calculate perimeter of a triangle.
Look at the figure given alongside. The sides LM, MN and NL of the given a c
triangle are of lengths a, b and c, respectively.

Perimeter of triangle LMN = Sum of all the three sides M N
b
= LM + MN + NL
= a + b + c

Perimeter of a triangle = Side + Side + Side

Example 6: Find the perimeter of a triangle whose sides measure 4 cm, 6 cm and 5 cm.
A
Solution: AB = 4 cm, BC = 6 cm and CA = 5 cm
Perimeter of the given triangle = AB + BC + CA
4 cm 5 cm
= 4 cm + 6 cm + 5 cm = 15 cm
So, the perimeter of the given triangle is 15 cm. B C
6 cm
Example 7: The sides of a triangular park measure 30 m, 25 m and 20 m. Find the length of the
wire required for fencing the park. Also, find the cost of fencing the triangular park
at the rate of ` 2 per metre.
Solution: Perimeter of the triangular park = Sum of all the three sides
= AB + BC + CA A

= 30 m + 25 m + 20 m = 75 m
30 m 20 m
 Length of the wire required for fencing = 75 m

Cost of fencing 1 m = ` 2 B C
25 m
 Cost of fencing 75 m = ` 2 × 75 = ` 150
So, the length of the wire required for fencing the triangular park is 75 m and the
cost of fencing it is at the rate of ` 2 per metre is ` 150.

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