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Subject – Mathematics

Chapter 9 – AREA & PERIMETER

Sub-topic 6 : FINDING THE MISSING SIDE

1. When the perimeter of a square is given, the formula for finding out the
length of each side is as follows:
S = P/4 or ¼ x perimeter

Where, S = length of each side
P = Perimeter
Example: If the perimeter of a square is 92 cm, find its sides.
Solution:
Perimeter = 4 × side
Or, Side of Square = ¼ × perimeter

So, side of the square = 92/4 = 23 cm
2. When the perimeter and breadth of a rectangle is given, the formula for
finding the length of the rectangle is as follows:
L = P/2 – B
Where, L = length
B = breadth

P = perimeter
Example: There is a rectangular fence surrounding a park. The perimeter of the
fence is 16ft. What is the length of the fence if the width is 5ft?

Solution: Given,
Perimeter of the park = 16ft
Width of the park = 5ft
Let L be the length of the park.
From the formula, we know,

Perimeter, P = 2(length + width)
Substituting the values, we get;
L = P/2 – B
= 16/2 – 5

= 8 – 5
= 3ft
Hence, the Length of the park = 3ft.

3. When the perimeter and length of a rectangle is given, the formula for
finding the breadth of the rectangle is as follows:
B = P/2 – L