10
1. Revision
Description


Recall how to
calculate
perimeter of
different
figures when
lengths of
boundary sides
are given.
Reflect and
Review


Recall how to
calculate area
of figures
formed on
square grid of
side 1 cm.
2. Perimeter
Description
The perimeter is
the length of the
boundary of a
closed figure.
Teasers
1) Find the perimeter of the
figure given below:
1) 32.5 cm
2) 5 sq. cm
To find the area
of an irregular
shape, first we
count the full
squares inside it.
Then we count all
the other squares 2) Find the area of the figure
given below:
which have more
than half the area
covered.
Reflect and
Review
Perimeter of a Rectangle
Perimeter of a rectangle
= 2 × ( length + breadth)
= 2 × ( l + b)
Answers
To find the
perimeter of a
rectangle of length
7.2 cm and breadth
3.5 cm:
Teasers
Answer
s
1) Find the perimeter of the
figure given below:
1) 60 cm
2) 198 m
21 cm
9 cm
1
Perimeter of
rectangle
= 2 × ( l + b)
= 2 x (7.2 + 3.5) cm
= 21.4 cm
Perimeter of a Square
Perimeter of a square
= 4 × side
=4×s
To find the
perimeter of a
rectangle of side 6.4
cm:
2) Find the perimeter of a
plot in the shape of a
rectangle, having length of
65 m and breadth of 34 m.
1) Find the perimeter of the 1) 60 cm
figure given below
2) 42 cm
15cm
Perimeter of square
=4×s
= (4 x 6.4) cm
= 25.6 cm
15cm
2) A flash card is made of a
small piece of cardboard
paper in the shape of a
square of side 10.5 cm. Find
its perimeter.
3. Area
Description
Reflect and
Review
The amount of surface Area is measured in
occupied by a closed square units.
figure is called its area.
1. If dimensions are in
mm, unit of area
will be sq. mm or
mm2.
2. If dimensions are in
cm, unit of area
will be sq. cm or
cm2.
3. If dimensions are in
m, unit of area will
be sq. m or m2.
4. If dimensions are in
km, unit of area
will be sq. km or
km2.
2
Teasers
Answers
Area of a Rectangle
Area of a rectangle
= Length × Breadth
=l×b
1) Find the area of a 1) 14 sq. m
To find the area of a
rectangle of length
rectangle of length 7
5 m and breadth 2.8 2) 378 sq. cm
cm and breadth 4 cm:
m.
Area of rectangle
=l×b
= 7 x 4 sq. cm
= 28 sq. cm
Area of a Square
Area of a square
= Side × Side
=s×s
Area of a Triangle
Area of a triangle
= ½ × area of the rectangle
2) What will be the
area of a photo
frame of length 27
cm and breadth 14
cm?
1) A square tile is of 1) 576 sq. cm
To find the area of a
side 24 cm. Find its
square of length 6 cm:
area.
2) 17 m
Area of square
=sxs
= (6 x 6) sq. cm
= 36 sq. cm
2) Find the side of a
square of area 289
sq. m.
To find the area of the
triangle in the figure
below:
Find the area of the
following triangles, if
each small square has
side 1 unit:
1) 4.5 sq.
units
2) 2.5 sq.
units
1)
Area of the rectangle
= 2 × 3 = 6 sq. units
2)
Since the triangle is
half of the rectangle,
its area will also be half
the area of the
rectangle.
∴ Area of the triangle
in the given figure
= (½ × 6) sq. units
= 3 sq. units
3
4. Area of Irregular Shapes
Description
Reflect and Review
The area of an irregular
shape can only be
approximately estimated,
not exactly calculated.

Step 1: Place the
shape on a 1 × 1
square grid.

Step 2: Count the
number of complete
unit squares covered
by the shape.

Step 3: Count the
number of unit
squares which are
more than halfcovered by the
shape.

4
Step 4: Add all the
unit squares obtained
in Step 2 and Step 3
to get the total area
of the irregular
shape.
Teasers
Answers
12 sq. units
To find the area of the Find the area of the
shape in the figure below:
shape in the figure
below:
Number of complete unit
squares covered is 2.
Number of unit squares
which are more than half
covered is 5.
∴ Total area covered by the
figure is (5 + 2) sq. units = 7
sq. units.