1. Perimeter given Find missing side

2. Example 1: The perimeter of a rectangle is 36 m. Find the length if the
breadth is 10 m.
b=10m
p=36
l=?
Solution:
Given:
Breadth(b) = 10 m and Perimeter (p)= 36 m
To find: Breadth of a rectangle
Perimeter of rectangle = 2 x (length + breadth)
= 2 x (length + 10)
2 x (length + 10) = 36
length + 10 =
Length = 18
Length = 18 – 10 = 8 m
(Transposing 2 to the RHS)
Ans: Length = 8m

3. a=? Example 2: Find the sides of a square if its perimeter is 20 cm?
Solution:
Given: Perimeter of a square(p) = 20 cm
To find: Side of a square(a)
Perimeter of square = 4 x a
20 = 4 x a
4 x a = 20
a =
a = 5 cm
p=20
a=?
Ans: Side = 5 cm

4. Example 3: The scalene triangle has 40 cm as its perimeter and whose two
sides are 13 cm and 15 cm, find the third side.
Solution:
Given: Perimeter of a triangle(p) = 40 cm
Two sides of triangle a=13cm , b= 15cm
To find: Third side (c)
Perimeter of triangle = a + b +c
40 = c
40 = c
c =
c = 12 cm
15 cm
13 cm
c=?
l = 40cm
Ans: Third side = 12 cm

5. Ans: side of equilateral triangle = 43cm
Example 4: Find the side of the equilateral triangle of perimeter 129 cm.
Solution:
Given: Perimeter of a equilateral triangle(p) = 129 cm
To find: side of equilateral triangle
In equilateral triangle all three sides are same
Let the side of equilateral sides be a
∴ Perimeter of equilateral triangle = a + a +a
129 = 3 x a
a =
a = 43 cm
Ans: side of equilateral triangle = 43cm

6. Try these Find the side of a square whose perimeter is 24 cm
Find the side of equilateral triangle whose
perimeter is 123 cm