Page 193 - Touchpad Mathematics_Ver1.0_C5

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example 5. The perimeter of a rectangle is 72 metres and its length is 21 metres.
Find its breadth.

Solution. Perimeter of the rectangle = 2(Length + Breadth)
72 = 2(21 + Breadth)

72 ÷ 2 = 21 + Breadth

36 = 21 + Breadth
So, Breadth = 36 – 21 = 15 m.

Hence, the breadth of the rectangle is 15 m.

Perimeter of a Square

In the given figure, ABCD is a square. We know that all four sides
of a square are equal.

So, Perimeter of a square = AB + BC + CD + DA
= AB + AB + AB + AB
[Since AB = BC = CD = DA]

= 4 × AB
Hence, Perimeter of a square = 4 × side.

example 6. Find the perimeter of a square where each side is 5 cm.
Solution. Here, side = 5 cm

Perimeter = 4 × side = 4 × 5 cm = 20 cm
Thus, the perimeter of the square is 20 cm.

example 7. A square garden has a fencing of length 48 m. What is the length of one
side of the garden?
Solution. Length of fencing = Perimeter of the square garden

Perimeter of the square = 4 × side
48 m = 4 × side

Side = (48 ÷ 4) m = 12 m
Hence, each side of the garden is 12 m.
example 8. Find the cost of framing a square picture whose length is 18 cm, if the
frame is bought at the rate of `5 per cm.

Solution. Here, length = 18 cm
Perimeter of the picture = 4 × side

= 4 × 18 cm = 72 cm
Now, the cost of a 1 cm long frame = `5

So, the cost of a 72 cm long frame = `5 × 72 = `360.

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Perimeter and Area