Maharashtra Board Class 4 Maths Part Two Chapter 12 Perimeter and Area PDF Download

12. Perimeter And Area

Perimeter

Sita: Salma, will you come to the market with me to buy lace?

Salma: Why do you need lace?

Sita: I have a handkerchief. I want to trim it with lace.

Salma: How much lace do you need?

Sita: Oh yes! How much lace do I need?

Salma: Let us take a spool of thread. Hold one end of the thread at one corner of the handkerchief. Then, slowly unwind the thread along all four of its sides until you reach the first corner. Cut it there. You will know how much lace you need by the length of the thread you have cut off.

ABCD is a square handkerchief. The sum of the length of sides AB, BC, CD and DA is the length of lace needed. This length is called the perimeter of the handkerchief.

The perimeter of a square is the sum of the length of all four sides of the square.

A fence of a single wire has to be put around a rectangular field. We have to find out the length of the wire needed. The sum of the lengths of all four sides of the rectangular field will tell us the length of wire needed.

The perimeter of a rectangle is the sum of the length of all four sides of the rectangle.

This is a triangle made of wire. To find out the length of the wire needed to make it, we will straighten out the wire and measure its length. This length will be the sum of the length of the three sides of the triangle.

The perimeter of a triangle is the sum of the length of all three sides of the triangle.

This figure shows a rectangle whose sides are 3cm, 2cm, 3cm and 2 cm. Let us find out its perimeter.

The perimeter of a rectangle is the sum of the length of all four of its sides.

\(3 + 2 + 3 + 2 = 10.\)

Therefore, the perimeter of this rectangle is 10 cm.

Teacher's Note

Perimeter means the distance around a shape. When your mother makes a border around a saree, she is finding the perimeter of the cloth.

Exam Trick

Remember: Perimeter = going all around. Just like you walk around your school ground, perimeter is the total distance around any shape.

Points to Remember

Perimeter is the total distance around a closed shape.
For a square, add all 4 sides.
For a rectangle, add all 4 sides.
For a triangle, add all 3 sides.
Perimeter helps us know how much wire, lace, or rope we need.

The figure alongside is a square and all of its sides are 2 cm long. Let us find the perimeter of the square. The perimeter of a square is the sum of the length of its four sides.

\(2 + 2 + 2 + 2 = 8.\)

Therefore, the perimeter of the square = 8 cm.

The sides of the triangle here are 4 cm, 5 cm and 6 cm long. Let us find out the perimeter of the triangle. The perimeter of a triangle is the sum of the length of all three of its sides.

\(4 + 5 + 6 = 15.\)

Therefore, the perimeter of this triangle = 15 cm.

Exercise

1. Find the perimeter of the figures given below.

(1) Perimeter = ___ cm

(2) Perimeter = ___ cm

(3) Perimeter = ___ cm

(4) Perimeter = ___ cm

(5) Perimeter = ___ cm

2. The sides of a rectangular field are 150m, 120m, 150m and 120m. Find the perimeter of the field.

Teacher's Note

You can find perimeter by walking around the boundary of your classroom and counting steps. This is a fun way to understand what perimeter means.

Exam Trick

For rectangles, remember: Add length twice and width twice. Or use the formula: Perimeter = 2 × (length + width).

Points to Remember

A square has all sides equal.
A rectangle has opposite sides equal.
Perimeter tells us the distance around the outside of a shape.
Different shapes have different number of sides.
We add all sides to find perimeter.

Area

Saina: I have more chikki than you.

Virat: I have more chikki than you.

Sumatai: Stop! Don't fight. Saina, why don't you count the number of chikki squares you have?

Saina: I have 16 squares of chikki.

Sumatai: Now, Virat, you count the number of chikki squares that you have.

Virat: I have 16 squares of chikki, too.

Sumatai: Now tell me, who has more chikki?

Saina: We were fighting over nothing. Tai, We both have the same amount of chikki.

Sumatai: That's right. But, let me explain it to you properly. The thickness of the squares of chikki you both have is the same. So, let us measure their surfaces. There are 16 squares of equal measure on both your slabs. Therefore, you both got the same amount of chikki.

On any surface, the measure of the place occupied by a figure is the area of that figure.

The measure of a figure should be the same no matter who measures it. Hence, 'a square of side 1 cm' is used as the standard unit of measurement of area. The area of a figure is given in square centimetres (sq cm).

To find out the area of this rectangular piece of paper, let us count the number of squares with sides of 1 cm on the paper. There are 10 such squares on the paper.

Therefore, the area of the paper is 10 sq cm.

To find out the area of the shape given alongside, let us count the number of squares with sides 1 cm, in it.

Area of the shape = number of squares = 9

Therefore, area of the shape = 9 sq cm.

Teacher's Note

Area is how much space something takes up. When your mother buys cloth for a saree, she buys it based on how much space the cloth covers, not just how long it is.

Exam Trick

Remember: Area = how much space inside. Just like a floor of your room has an area, every flat shape has an area. Count the squares to find area.

Points to Remember

Area is the space inside a closed shape.
We measure area in square centimetres (sq cm).
A square with 1 cm sides has an area of 1 sq cm.
We can find area by counting small squares.
Area and perimeter are different things.

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