Page 168 - Math Skill - 5

166 Maths

Perimeter
The distance around a closed figure or outer boundary of a closed figure is known as the
perimeter of the figure. Unit of perimeter is same as the unit of length or breadth.

Perimeter of a rectangle = 2 × (length + breadth)
Perimeter of a square = 4 × side

Perimeter of a Rectangle

In the rectangle shown, the perimeter will be the sum of all its sides.
Therefore, perimeter = l + b + l + b = l + l + b + b
= 2 × l + 2 × b

= 2 (l + b)

Perimeter of a rectangle = 2 (length + breadth)

Perimeter of a Square

In the square shown, the perimeter will be the sum of all its sides.
Therefore, perimeter = s + s + s + s = 4s

Perimeter of a square = 4 × side

Let’s Attempt

Example 1: Find the perimeter of a rectangle whose length is 6 cm and breadth is 3.5 cm.

Solution: Length of the rectangle = 6 cm

Breadth of the rectangle = 3.5 cm
Perimeter of the rectangle = 2 (length +breadth)
= 2 (6 + 3.5) cm

= 2 × 9.5 cm = 19 cm
Hence, the perimeter of the rectangle is 19 cm.

Example 2: Find the perimeter of a square whose each side measures 10 cm.
Solution: Side of the square = 10 cm Fact-o-meter

Perimeter of the square = 4 × side The length and breadth
= 4 × 10 cm must have the same unit

= 40 cm while calculating perimeter.

Exercise 13.1

1. The length and breadth of some rectangles are given. Find their perimeter using the formula.

(a) l = 42 cm, b = 15 cm (b) l = 3.5 m, b = 3 m (c) l = 2.125 m, b = 1.250 m