NCERT Textbook - Mensuration Class 6 Notes | EduRev

Mathematics (Maths) Class 6

Created by: Praveen Kumar

Class 6 : NCERT Textbook - Mensuration Class 6 Notes | EduRev

 Page 1


When we talk about some plane figures as shown below we think of their
regions and their boundaries. We need some measures to compare them. We
look into these now.
10.2 Perimeter
Look at the following figures (Fig. 10.1). Y ou can make them with a wire or a string.
If you start from the point S in each case and move along the line segments
then you again reach the point S. You have made a complete round of the
10.1 Introduction
Chapter 10
M M Me e en n ns s su u ur r ra a at t ti i io o on n n
Page 2


When we talk about some plane figures as shown below we think of their
regions and their boundaries. We need some measures to compare them. We
look into these now.
10.2 Perimeter
Look at the following figures (Fig. 10.1). Y ou can make them with a wire or a string.
If you start from the point S in each case and move along the line segments
then you again reach the point S. You have made a complete round of the
10.1 Introduction
Chapter 10
M M Me e en n ns s su u ur r ra a at t ti i io o on n n
MATHEMATICS
206
shape in each case (a), (b) & (c). The distance covered is equal to the length of
wire used to draw the figure.
This distance is known as the perimeter of the closed  figure. It is the
length of the wire needed to form the figures.
The idea of perimeter is widely used in our daily life.
 A farmer who wants to fence his field.
 An engineer who plans to build a compound wall on all sides of a house.
 A person preparing a track to conduct sports.
All these people use the idea of ‘perimeter’.
Give five examples of situations where you need to know the perimeter.
Perimeter is the distance covered along the boundary forming a closed
figure when you go round the figure once.
1. Measure and write the length of the four sides of the top of your
study table.
AB = ____ cm
BC = ____ cm
CD = ____ cm
DA = ____ cm
Now, the sum of the lengths of the four sides
= AB + BC + CD + DA
= ___ cm +___ cm +___ cm +___ cm
= _____ cm
What is the perimeter?
2. Measure and write the lengths of the four sides of a page of your
notebook. The sum of the lengths of the four sides
= AB + BC + CD + DA
= ___ cm +___ cm +___ cm +___ cm
= _____ cm
What is the perimeter of the page?
3. Meera went to a park 150 m long and 80 m wide. She took one
complete round on its boundary. What is the distance covered by
her?
Page 3


When we talk about some plane figures as shown below we think of their
regions and their boundaries. We need some measures to compare them. We
look into these now.
10.2 Perimeter
Look at the following figures (Fig. 10.1). Y ou can make them with a wire or a string.
If you start from the point S in each case and move along the line segments
then you again reach the point S. You have made a complete round of the
10.1 Introduction
Chapter 10
M M Me e en n ns s su u ur r ra a at t ti i io o on n n
MATHEMATICS
206
shape in each case (a), (b) & (c). The distance covered is equal to the length of
wire used to draw the figure.
This distance is known as the perimeter of the closed  figure. It is the
length of the wire needed to form the figures.
The idea of perimeter is widely used in our daily life.
 A farmer who wants to fence his field.
 An engineer who plans to build a compound wall on all sides of a house.
 A person preparing a track to conduct sports.
All these people use the idea of ‘perimeter’.
Give five examples of situations where you need to know the perimeter.
Perimeter is the distance covered along the boundary forming a closed
figure when you go round the figure once.
1. Measure and write the length of the four sides of the top of your
study table.
AB = ____ cm
BC = ____ cm
CD = ____ cm
DA = ____ cm
Now, the sum of the lengths of the four sides
= AB + BC + CD + DA
= ___ cm +___ cm +___ cm +___ cm
= _____ cm
What is the perimeter?
2. Measure and write the lengths of the four sides of a page of your
notebook. The sum of the lengths of the four sides
= AB + BC + CD + DA
= ___ cm +___ cm +___ cm +___ cm
= _____ cm
What is the perimeter of the page?
3. Meera went to a park 150 m long and 80 m wide. She took one
complete round on its boundary. What is the distance covered by
her?
MENSURATION
207
4. Find the perimeter of the following figures:
(a)
(b)
(c)
(d)
So, how will you find the perimeter of any closed figure made up entirely
of line segments? Simply find the sum of the lengths of all the sides (which
are line segments).
Perimeter = AB + BC + CD + DA
= __+__+__+__+__+ __
= ______
Perimeter = AB + BC + CD + DA
= __ + __ + __+
= ______
Perimeter
=
AB + BC + CD + DE
+ EF + FG + GH +HI
+ IJ + JK + KL + LA
=
__ + __ +__ + __ + __ +
__ + __ + __ +__+ __
+ __ + __
=
______
Perimeter
=
AB + BC + CD + DE + EF
+ FA
=
__ + __ + __ + __ + __ + __
=
______
Page 4


When we talk about some plane figures as shown below we think of their
regions and their boundaries. We need some measures to compare them. We
look into these now.
10.2 Perimeter
Look at the following figures (Fig. 10.1). Y ou can make them with a wire or a string.
If you start from the point S in each case and move along the line segments
then you again reach the point S. You have made a complete round of the
10.1 Introduction
Chapter 10
M M Me e en n ns s su u ur r ra a at t ti i io o on n n
MATHEMATICS
206
shape in each case (a), (b) & (c). The distance covered is equal to the length of
wire used to draw the figure.
This distance is known as the perimeter of the closed  figure. It is the
length of the wire needed to form the figures.
The idea of perimeter is widely used in our daily life.
 A farmer who wants to fence his field.
 An engineer who plans to build a compound wall on all sides of a house.
 A person preparing a track to conduct sports.
All these people use the idea of ‘perimeter’.
Give five examples of situations where you need to know the perimeter.
Perimeter is the distance covered along the boundary forming a closed
figure when you go round the figure once.
1. Measure and write the length of the four sides of the top of your
study table.
AB = ____ cm
BC = ____ cm
CD = ____ cm
DA = ____ cm
Now, the sum of the lengths of the four sides
= AB + BC + CD + DA
= ___ cm +___ cm +___ cm +___ cm
= _____ cm
What is the perimeter?
2. Measure and write the lengths of the four sides of a page of your
notebook. The sum of the lengths of the four sides
= AB + BC + CD + DA
= ___ cm +___ cm +___ cm +___ cm
= _____ cm
What is the perimeter of the page?
3. Meera went to a park 150 m long and 80 m wide. She took one
complete round on its boundary. What is the distance covered by
her?
MENSURATION
207
4. Find the perimeter of the following figures:
(a)
(b)
(c)
(d)
So, how will you find the perimeter of any closed figure made up entirely
of line segments? Simply find the sum of the lengths of all the sides (which
are line segments).
Perimeter = AB + BC + CD + DA
= __+__+__+__+__+ __
= ______
Perimeter = AB + BC + CD + DA
= __ + __ + __+
= ______
Perimeter
=
AB + BC + CD + DE
+ EF + FG + GH +HI
+ IJ + JK + KL + LA
=
__ + __ +__ + __ + __ +
__ + __ + __ +__+ __
+ __ + __
=
______
Perimeter
=
AB + BC + CD + DE + EF
+ FA
=
__ + __ + __ + __ + __ + __
=
______
MATHEMATICS
208
Fig 10.3
Find the perimeter of the following rectangles:
Length of Breadth of Perimeter by adding Perimeter by
rectangle rectangle all the sides   2 × (Length + Breadth)
25 cm 12 cm = 25 cm + 12 cm = 2 ×(25 cm + 12 cm)
+ 25 cm + 12 cm = 2 × (37 cm)
= 74 cm = 74 cm
0.5 m 0.25 m
18 cm 15 cm
10.5 cm 8.5 cm
10.2.1 Perimeter of a rectangle
Let us consider a rectangle ABCD (Fig 10.2)
whose length and breadth are 15 cm and 9 cm
respectively. What will be its perimeter?
Perimeter of the rectangle = Sum of the
lengths of its four sides.
= AB + BC + CD + DA
= AB + BC + AB + BC
= 2 × AB + 2 × BC
= 2 × (AB + BC)
= 2 × (15cm + 9cm)
= 2 × (24cm)
= 48 cm
Hence, from the said example, we notice that
Perimeter of a rectangle = length + breadth + length + breadth
i.e. Perimeter of a rectangle = 2 × (length + breadth)
Let us now see practical applications of this idea :
Example 1 : Shabana wants to put a lace border all around a rectangular table
cover (Fig 10.3), 3 m long and 2 m wide. Find the length of the lace required
by Shabana.
Solution : Length of the rectangular table cover = 3 m
Breadth of the rectangular table cover = 2 m
Shabana wants to put a lace border all around the
table cover. Therefore, the length of the lace required
will be equal to the perimeter of the rectangular table
cover.
Remember that
opposite sides of a
rectangle are equal
so AB = CD,
AD = BC
Fig 10.2
Page 5


When we talk about some plane figures as shown below we think of their
regions and their boundaries. We need some measures to compare them. We
look into these now.
10.2 Perimeter
Look at the following figures (Fig. 10.1). Y ou can make them with a wire or a string.
If you start from the point S in each case and move along the line segments
then you again reach the point S. You have made a complete round of the
10.1 Introduction
Chapter 10
M M Me e en n ns s su u ur r ra a at t ti i io o on n n
MATHEMATICS
206
shape in each case (a), (b) & (c). The distance covered is equal to the length of
wire used to draw the figure.
This distance is known as the perimeter of the closed  figure. It is the
length of the wire needed to form the figures.
The idea of perimeter is widely used in our daily life.
 A farmer who wants to fence his field.
 An engineer who plans to build a compound wall on all sides of a house.
 A person preparing a track to conduct sports.
All these people use the idea of ‘perimeter’.
Give five examples of situations where you need to know the perimeter.
Perimeter is the distance covered along the boundary forming a closed
figure when you go round the figure once.
1. Measure and write the length of the four sides of the top of your
study table.
AB = ____ cm
BC = ____ cm
CD = ____ cm
DA = ____ cm
Now, the sum of the lengths of the four sides
= AB + BC + CD + DA
= ___ cm +___ cm +___ cm +___ cm
= _____ cm
What is the perimeter?
2. Measure and write the lengths of the four sides of a page of your
notebook. The sum of the lengths of the four sides
= AB + BC + CD + DA
= ___ cm +___ cm +___ cm +___ cm
= _____ cm
What is the perimeter of the page?
3. Meera went to a park 150 m long and 80 m wide. She took one
complete round on its boundary. What is the distance covered by
her?
MENSURATION
207
4. Find the perimeter of the following figures:
(a)
(b)
(c)
(d)
So, how will you find the perimeter of any closed figure made up entirely
of line segments? Simply find the sum of the lengths of all the sides (which
are line segments).
Perimeter = AB + BC + CD + DA
= __+__+__+__+__+ __
= ______
Perimeter = AB + BC + CD + DA
= __ + __ + __+
= ______
Perimeter
=
AB + BC + CD + DE
+ EF + FG + GH +HI
+ IJ + JK + KL + LA
=
__ + __ +__ + __ + __ +
__ + __ + __ +__+ __
+ __ + __
=
______
Perimeter
=
AB + BC + CD + DE + EF
+ FA
=
__ + __ + __ + __ + __ + __
=
______
MATHEMATICS
208
Fig 10.3
Find the perimeter of the following rectangles:
Length of Breadth of Perimeter by adding Perimeter by
rectangle rectangle all the sides   2 × (Length + Breadth)
25 cm 12 cm = 25 cm + 12 cm = 2 ×(25 cm + 12 cm)
+ 25 cm + 12 cm = 2 × (37 cm)
= 74 cm = 74 cm
0.5 m 0.25 m
18 cm 15 cm
10.5 cm 8.5 cm
10.2.1 Perimeter of a rectangle
Let us consider a rectangle ABCD (Fig 10.2)
whose length and breadth are 15 cm and 9 cm
respectively. What will be its perimeter?
Perimeter of the rectangle = Sum of the
lengths of its four sides.
= AB + BC + CD + DA
= AB + BC + AB + BC
= 2 × AB + 2 × BC
= 2 × (AB + BC)
= 2 × (15cm + 9cm)
= 2 × (24cm)
= 48 cm
Hence, from the said example, we notice that
Perimeter of a rectangle = length + breadth + length + breadth
i.e. Perimeter of a rectangle = 2 × (length + breadth)
Let us now see practical applications of this idea :
Example 1 : Shabana wants to put a lace border all around a rectangular table
cover (Fig 10.3), 3 m long and 2 m wide. Find the length of the lace required
by Shabana.
Solution : Length of the rectangular table cover = 3 m
Breadth of the rectangular table cover = 2 m
Shabana wants to put a lace border all around the
table cover. Therefore, the length of the lace required
will be equal to the perimeter of the rectangular table
cover.
Remember that
opposite sides of a
rectangle are equal
so AB = CD,
AD = BC
Fig 10.2
MENSURATION
209
Now, perimeter of the rectangular table cover
= 2 × (length + breadth) = 2 × (3 m + 2 m) = 2 × 5 m = 10 m
So, length of the lace required is 10 m.
Example 2 : An athlete takes 10 rounds of a rectangular park, 50 m long and
25 m wide. Find the total distance covered by him.
Solution : Length of the rectangular park = 50 m
      Breadth of the rectangular park = 25 m
Total distance covered by the athlete in one round will be the perimeter of
the park.
Now, perimeter of the rectangular park
= 2 × (length + breadth)= 2 × (50 m + 25 m)
= 2 × 75 m = 150 m
So, the distance covered by the athlete in one round is 150 m.
Therefore, distance covered in 10 rounds = 10 × 150 m = 1500m
The total distance covered by the athlete is 1500 m.
Example 3 : Find the perimeter of a rectangle whose length and breadth are
150 cm and 1 m respectively.
Solution  : Length = 150 cm
Breadth = 1m = 100 cm
Perimeter of the rectangle
= 2 × (length + breadth)
= 2 × (150 cm + 100 cm)
= 2 × (250 cm) = 500 cm = 5 m
Example 4 : A farmer has a rectangular field
of length and breadth 240 m and 180 m
respectively. He wants to fence it with 3
rounds of rope as shown in figure 10.4.
What is the total length of rope he must use?
Solution : The farmer has to cover three
times the perimeter of that field. Therefore,
total length of rope required is thrice its perimeter.
Perimeter of the field = 2 × (length + breadth)
= 2 × ( 240 m + 180 m)
= 2 × 420 m = 840 m
Total length of rope required  = 3 × 840 m = 2520 m
150 cm
150 cm
1m
1m
Fig 10.4
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