10-2 Estimating and Finding Area Course 1 Warm Up Warm Up Lesson Presentation Lesson Presentation Problem of the Day Problem of the Day

10-2 Estimating and Finding Area

Course 1

Warm UpWarm Up

Lesson PresentationLesson Presentation

Problem of the DayProblem of the Day

Warm Up

1. What is the perimeter of a square with side lengths of 15 in.?

2. What is the perimeter of a rectangle with length 16 cm and width 11 cm?

60 in.

54 cm

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Problem of the Day

Two wibbles equal four wabbles, and eight wabbles equal two bibbles. If a square has a perimeter of 16 wibbles, what is its area in square bibbles?

4 square bibbles

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Learn to estimate the area of irregular figures and to find the area of rectangles, triangles, and parallelograms.

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Vocabulary

area

Insert Lesson Title Here

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The area of a figure is the amount of surface it covers. We measure area in square units.

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Additional Example 1: Finding the Area of an Irregular Figure

Find the area of the rectangle.

Count full squares: 19 red squares.

Count almost-full squares: 9 blue squares.Count squares that are about half-full: 4 green squares = 2 full squares.Do not count almost empty yellow squares.Add. 19 + 9 + 2 = 30

The area of the figure is about 30 mi .2

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Try This: Example 1

Estimate the are of the figure.

Count full squares: 11 red squares.

Count almost-full squares: 5 green squares.Count squares that are about half-full: 4 blue squares = 2 full squares.Do not count almost empty yellow squares.Add. 11 + 5 + 2 = 18

The area of the figure is about 18 mi .2

= mi2

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Additional Example 2: Estimating the Area of a Rectangle

Find the area of the figure.

Write the formula.

Substitute 15 for l.Substitute 9 for w.

A = lw

A = 15 • 9

A = 135

The area is about 135 in2.

15 in.

9 in.

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Try This: Example 2

Find the area of the figure.

Write the formula.

Substitute 13 for l.Substitute 7 for w.

A = lw

A = 13 • 7

A = 91

The area is about 91 in2.

13 in.

7 in.

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You can use the formula for the area of a rectangle to write a formula for the area of a parallelogram. Imagine cutting off the triangle drawn in the parallelogram and sliding it to the right to form a rectangle.

The area of a parallelogram = bh. The area of a rectangle = lw.

The base of the parallelogram is the length of the rectangle. The height of the parallelogram is the width of the rectangle.

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Additional Example 3: Finding the Area of a Parallelogram

Find the area of the parallelogram.

Write the formula.

Multiply.

A = bh

2 ft12

A = 2 • 112__ 1

4__ Substitute 2 for b

and 1 for h.

12__

14__

A = •52__ 5

4__

A = or 325 8

___ 18__

The area is 3 ft2. 18__

14

1 ft

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Try This: Example 3

Find the area of the parallelogram.

Write the formula.

Multiply.

A = bh

A = 1 • 312__ 1

2__ Substitute 1 for b

and 3 for h.

12__

12__

A = •32__ 7

2__

A = or 521 4

___ 14__

The area is 5 ft2.14__

11 ft2

13 ft2

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You can make a parallelogram out of two congruent triangles.

The area of each triangle is half the area of the parallelogram, so the formula for the area of a

triangle is A = bh.12__

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Additional Example 4: Finding the Area of a Triangle

Find the area of the triangle.

Write the formula.

Substitute 9.6 for b. Substitute 2.9 for h.

Multiply.

The area is 13.92 cm2.

A = 13.92

A = bh12__

A = (9.6 • 2.9)12__

A = (27.84)12__

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Try This: Example 4

Find the area of the triangle.

Write the formula.

Substitute 8.5 for b. Substitute 3.4 for h.

Multiply.

The area is 14.45 cm2.

3.4 cm

8.5 cm

A = 14.45

A = bh12__

A = (8.5 • 3.4)12__

A = (28.9)12__

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Lesson Quiz

Find the area of each figure.

1. 2.

3. What is the area of a parallelogram with base

16 in. and height 10 in.?

4. What is the area of a triangle with base 10 in.

and height 7 in.?

Insert Lesson Title Here

4.5 m

9.2 m41.4 m2 24 ft2

160 in2

35 in2

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Documents

10-2 Estimating and Finding Area Course 1 Warm Up Warm Up Lesson Presentation Lesson Presentation Problem of the Day Problem of the Day