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Examples of Perimeter

Let us now look at some examples of perimeter calculations for various shapes.

 

1. What is the perimeter of a square with side = 5 cm?  

square with side=5 cmThe formula to calculate the perimeter of a square = 4s (where s is the length of the side of the square)

So the perimeter of the square = 5 + 5 + 5 + 5 = 20 cm, or

  =  4 x 5  = 20 cm

 

2. The perimeter of this square is 36 cm. We need to find k.  perimeter of square=36 cm

Perimeter of a square = 4k = 36 cm

So k = 36 ÷ 4

  =  9 cm

 

3. The perimeter of this rectangle is 28 mm, what is t?   perimeter of rectangle=28 mm

Perimeter of a rectangle = 2(l + b)  =  28 mm

So 2(9 + t) = 28

9 + t  =  14

t = 14 – 9  =  5 mm

So the breadth of the rectangle is 5 mm.

 

4. Calculate the perimeter of the triangle.    perimeter of triangle=18 cm

Perimeter of a triangle = sum of its sides

 = 4 + 5 + 9

 = 18 cm

 

5. Calculate the perimeter of these two quadrilaterals.    perimeter of quadrilateral=24 m

Perimeter of a quadrilateral = sum of its sides

 = 3 + 9 + 7 + 5

 = 24 m

 

Perimeter of quadrilateral = sum of its sides  perimeter of quadrilateral=23 m

 = 6 + 3 + 3 + 7 + 4

 = 23 m

 

 

6. What is the perimeter of this shape?     

perimeter of shape=28 unitsTo find the perimeter of this shape, we first need to find the lengths of the various unknown sides. Here the two unknown sides are the longest side (the base of the shape), and the short side to the right of the shape.

Length of the longest side = 4 + 4  =  8

Length of the shortest side = 6 – 3  =  3

So perimeter = 6 + 4 + 3 + 4+ 3 + 8

  =  28 units

 

7. What is the perimeter of this shape?     

perimeter of shape=53 unitsWe first need to find the length of the shortest side (unknown side)

The length of this side = 12 – (5 + 4)

   =  12 – 9

   = 3

Therefore perimeter =  3 + 12 + 3 + 5 + 7 + 3 + 7 + 4

  = (3 x 3) + 12 + 5 + (7 x 2) + 4

  = 9 + 12 + 5 + 14 + 4

  = 53 units

 

8. What is the perimeter of the figure?     

perimeter of shape=40 unitsIn this shape, we have four sides of equal length (= 7 units), and four other sides of equal length as well (= 3 units).

So perimeter = (4 x 7) + (4 x 3)

  =  28 + 12

  = 40 units