Page 172 - Start Up Mathematics_5

13

Perimeter, Area and Volume

Let's Recall …

The total length of the boundary of a plane closed figure is called its
perimeter.

1 Find the perimeter of the following figures.

5 cm 6 cm
3 cm 2 cm

(a) 3 cm 3 cm (b)
3 cm
4 cm
5 cm 5 cm

2 Find the perimeter of the following figures using a thread and ruler.

(a) (b) (c)

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

(a) (b) (c)

Perimeter

We have learnt to find the perimeter of plane closed Remember
figures using all sides, grid or thread. Now we will learn to
find the perimeter of some closed figures using formula. As perimeter is a length, its
unit is cm, m or km.

Perimeter of a rectangle

Let’s find the formula for perimeter of a rectangle using the definition of perimeter.
Perimeter of rectangle PQRS

= PQ + QR + RS + SP length (l) Q

= Length + Breadth + Length + Breadth
= (2 × Length) + (2 × Breadth) breadth (b) P breadth (b)

= 2 × (Length + Breadth) S R
length (l)
Perimeter of a rectangle = 2 × (l + b)

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