Multi-Part Lesson
8-2
Use a Formula to Find Area
A
PART
B
C
D
E
Justify the Formula
for Area of Rectangles
Main Idea
I will explore the
formula for area.
You have found the area of figures by counting the square units.
A formula can also be used to find area.
macmillanmh.com
Find a formula for area.
Materials
Step 1
centimeter cubes
EXP-Base-Ten
EXP-Base-Ten
EXP-Base-Ten
EXP-Base-Ten
blocks
blocks
blocks
1
blocks
1 1 1
centimeter
ruler
DFOUJNFUFST
Object
Base
Height
Area
sticky note
box
sticky notes
EXP-Centimeter ruler
book
Step 2
box
Make a table.
Copy the table below to record your findings.
EXP-Sticky notes
Step 3
Step 4
Measure the base and height of each object.
Use the centimeter ruler to
measure the base and height
of each object.
height
Find the area of each object.
Cover each object with the
base
centimeter cubes. Then count
the cubes to find the area.
Justify the formula for area.
Use the data to find how base
and height relate to area.
About It
1. What operation can you use with the base and height to equal
the area?
2. What is the formula for the area of a rectangle?
380
Chapter 8 Find Area
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Multi-Part Lesson
8-2
Use a Formula to Find Area
PART
A
Main Idea
I will use the area
formula to find the area
of rectangles.
New Vocabulary
square units
formula
B
C
D
E
Find Areas
of Rectangles
Area is the number of square units needed to cover a region
or figure without any overlap. It is measured in square units .
To find the area, you can count the square units, or you can
use a formula .
macmillanmh.com
Area of a Rectangle
Words
Formula
To find the area of a rectangle, multiply the
base (length) by the height (width).
A=b×h
h
b
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The Perez family wants to put the sandbox in their
backyard. What is the area of the bottom of the sandbox?
One Way:
Count
10 ft
5 ft
There are 50 square feet.
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Another Way:
Formula
Multiply the base by the
height to find the area.
A = base × height
A=b×h
A = 10 feet × 5 feet
A = 50 square feet
So, the area of the sandbox is 50 square feet.
Lesson 8-2 Use a Formula to Find Area
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When finding the area of a large object, you may want to use
the area formula instead of counting squares.
Area of a Rectangle
A
PHOTOS Judie is hanging
the photo at the right on a
wall. How much wall space
will the photo need?
Use the area formula.
5 in.
A = base × height
A = 7 inches × 5 inches
7 in.
A = 35 square inches
The photo will need 35 square inches of wall space.
Find the area of each rectangle. See Examples 1 and 2 (pp. 381–382)
1.
2.
3.
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4.
5.
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9 in.
8 ft
7m
4m
6.
12 ft
16 in.
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C08-064A-112056
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7. Mrs. Cole is buying a cover for her
8.
How would you find the
swimming pool. The pool’s sides are
area of a rectangle that has sides that
12 and 24 feet in length. What must
are 18 and 32 units long? Explain.
be the area of the pool cover?
382
Chapter 8 Find Area
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EXTRA
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2A
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See page R24.
Find the area of each rectangle. See Examples 1 and 2 (pp. 381–382)
9.
10.
11.
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12. C08-067A-112056
13.
14. C08-069A-112056
5 cm
7 km
9 mi
6 cm
10 km
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4 mi
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15. Ricky’s computer monitor is a C08-071A-112056
16. A rectangular playground
is 40 meters
rectangle. The side lengths are 12
by 10 meters. A bag of shredded tires
and 15 inches. What is the area of
covers 200 square meters and costs
the monitor?
$30. Find the total cost of covering the
playground with shredded tires.
Use the information to solve the problem.
a Class Pet
Having Having
a Class Pet
Remember,
we want to get
a guinea pig for
a class pet.
I also found out that
a guinea pig needs at
least 576 square inches
of living space.
So we need
to choose a glass
aquarium that is
the right size.
17. Which aquarium has a floor area of at least 576 square inches
and will take up the least amount of room in the classroom?
Explain.
18. OPEN ENDED Draw a rectangle with an area of 24 square units.
19.
Explain why two rectangles could each have
an area of 12 square units, but have different bases and heights.
Lesson 8-2 Use a Formula to Find Area
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