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

2. Estimating and Finding Area
Course 1
10-2
Estimating and Finding Area
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

3. Estimating and Finding Area
Course 1
10-2
Estimating and Finding Area
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

4. Estimating and Finding Area
Course 1
10-2
Estimating and Finding Area
Learn to estimate the area of irregular figures and to find the area of rectangles, triangles, and parallelograms.

5. Insert Lesson Title Here
Course 1
10-2
Estimating and Finding Area
Insert Lesson Title Here
Vocabulary
area

6. Estimating and Finding Area
Course 1
10-2
Estimating and Finding Area
The area of a figure is the amount of surface it covers. We measure area in square units.

7. Additional Example 1: Finding the Area of an Irregular Figure
Course 1
10-2
Estimating and Finding Area
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 = 30
The area of the figure is about 30 mi . 2

8. Estimating and Finding Area
Course 1
10-2
Estimating and Finding Area
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.
= mi2
Do not count almost empty yellow squares.
Add = 18
The area of the figure is about 18 mi . 2

9. Estimating and Finding Area
Course 1
10-2
Estimating and Finding Area

10. Additional Example 2: Estimating the Area of a Rectangle
Course 1
10-2
Estimating and Finding Area
Additional Example 2: Estimating the Area of a Rectangle
Find the area of the figure.
A = lw
15 in.
Write the formula.
A = 15 • 9
9 in.
Substitute 15 for l.
Substitute 9 for w.
A = 135
The area is about 135 in2.

11. Estimating and Finding Area
Course 1
10-2
Estimating and Finding Area
Try This: Example 2
Find the area of the figure.
A = lw
13 in.
Write the formula.
7 in.
A = 13 • 7
Substitute 13 for l.
Substitute 7 for w.
A = 91
The area is about 91 in2.

12. Estimating and Finding Area
Course 1
10-2
Estimating and Finding Area
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.

13. Additional Example 3: Finding the Area of a Parallelogram
Course 1
10-2
Estimating and Finding Area
Additional Example 3: Finding the Area of a Parallelogram
Find the area of the parallelogram.
A = bh
Write the formula.
Substitute 2 for b
and 1 for h. 1 2 __ 4 1
A = 2 • 1 1 2 __ 4
1 ft 4 1
2 ft
A = • 5 2 __ 4 2
Multiply.
A = or 3 25 8
___ 1 __
The area is 3 ft2. 1 8 __

14. Estimating and Finding Area
Course 1
10-2
Estimating and Finding Area
Try This: Example 3
Find the area of the parallelogram.
A = bh
Write the formula. 1
3 ft 2
A = 1 • 3 1 2 __
Substitute 1 for b
and 3 for h. 1 2 __ 1
1 ft 2
A = • 3 2 __ 7
Multiply.
A = or 5 21 4
___ 1 __
The area is 5 ft2. 1 4 __

15. Estimating and Finding Area
Course 1
10-2
Estimating and Finding Area
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. 1 2 __

16. Additional Example 4: Finding the Area of a Triangle
Course 1
10-2
Estimating and Finding Area
Additional Example 4: Finding the Area of a Triangle
Find the area of the triangle.
A = bh 1 2 __
Write the formula.
A = (9.6 • 2.9) 1 2 __
Substitute 9.6 for b. Substitute 2.9 for h.
A = (27.84) 1 2 __
Multiply.
A = 13.92
The area is cm2.

17. Estimating and Finding Area
Course 1
10-2
Estimating and Finding Area
Try This: Example 4
Find the area of the triangle.
A = bh 1 2 __
Write the formula.
3.4 cm
A = (8.5 • 3.4) 1 2 __
Substitute 8.5 for b. Substitute 3.4 for h.
8.5 cm
A = (28.9) 1 2 __
Multiply.
A = 14.45
The area is cm2.

18. Estimating and Finding Area Insert Lesson Title Here
Course 1
10-2
Estimating and Finding Area
Insert Lesson Title Here
Lesson Quiz
Find the area of each figure.
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.?
4.5 m
24 ft2
41.4 m2
9.2 m
160 in2
35 in2