Perimeter of Various Shapes Chapter Notes | Mathematics Olympiad Class 4 PDF Download

What is Perimeter?

Perimeter is the total length around the edge of a shape, like the distance around your favourite playground. To find it, you just add up the lengths of all the sides!

Meaning of Perimeter Formulas

Perimeter is all about adding side lengths! For any shape, even a strange one, the formula is simply the sum of all its straight sides. Imagine you trace the whole shape with a string - the total length of that string is the perimeter.  Regular shapes (like squares or triangles with equal sides) have shorter formulas because we can multiply one side length by the number of sides. But for any wonky shape, just add up every side to find the total distance around!

For Example, in the shape

 the sides are 10 cm, 8 cm, 8 cm, 4 cm, and 4 cm. Adding them all together gives us the total perimeter:

Perimeter = 10 cm + 8 cm + 8 cm + 4 cm + 4 cm = 34 cm

This approach works for any shape, regardless of how many sides it has or whether they are all the same length.

Examples Using Perimeter Formula

Example 1: Josie wants to add some lace as decoration to the borders of her tabletop sheet. The tabletop sheet is in the shape of a rectangle. The length of the tabletop sheet is 140 inches and the breadth is 95 inches. How long will be the lace needed?

Solution:
Given, length l = 140 in , breadth b = 95 in

The length of the lace = Perimeter of the sheet

 We know the Perimeter formula of a rectangle = 2(l+b).

Applying the values of length and breadth in this formula we have Perimeter = 2(l+b) = 2 (140 + 95) = 2  × 235 = 470 inches.

Therefore Josie will need 470 inches of lace.

Example 2: Determine the length of the side of the equilateral triangle, if its perimeter is 30 units.

Solution:
Given, the perimeter of the equilateral triangle = 30 

Let the length of the side of the equilateral triangle be a.

a is calculated using the perimeter formula of an equilateral triangle.

P = 3 × a

30 = 3 × a

a = 30/3

a = 10 units

Therefore, the length of the side of the equilateral triangle is 10 units.

Example 3: If the perimeter of a square is 74 units, find its side.

Solution: Given: Perimeter of square P = 74 units

Using the perimeter formula of a square, 

P = 4 × side units

74 = 4 × side 

Side = 74/4 

Side = 18.5 units

Therefore, the side of a square is 18.5 units