Finding Area Using Addition and Subtraction

1
Finding Area UsingAddition and Subtraction
2
20 ft
4 ft
How can we find the length of the rectangle?
How can we find the width of the rectangle?
What is the height of the trapezoid?
After we find each area what would we need to do?
What are base one and base two of the trapezoid?
What is the side length of the square?
2. substitute the formulas
3. substitute the numbers
Plan 1
1. Make a plan
12 ft
4 ft
N

• rectangle

trapezoid
square
( )
( ) ( )
Make a SMALL sketch of the new design.
l x w
F
( ) ( )
16)
(12
4
S
x 16
24
2
3
( ) ( )
4
16)
(12
x 16
24
2
x 16 ( )
( )
(28)
x 4
24
2
x 16 ( )
4. Follow PEMDAS to solve.
( )
112
24
2
)
24
x 16 (
56
( 56 )
24 x 16
16

24 x 16
72
72
384
312 ft2
4
384 ft2
Step 5. Area 312 ft2
5
What are the length and width of the first
rectangle?
What are the base and height of the triangle?
What are the length and width of the second
rectangle?
After we find each area what would we need to do?
3. substitute the numbers
1. Make a plan
2. substitute the formulas
Plan 2
N
rectangle

• rectangle

triangle

F
l x w
l x w

Make a SMALL sketch of the new design.
4
x 4
S
( ) ( ) (
)
20
x 12
16
x 4

6
4
x 4
( ) ( ) (
)
20
x 12
16
x 4

4
x 4
( ) ( )

240
16
x 4
4
x 4
( )
240
64
4. Follow PEMDAS to solve.
16
( )
240
64
240
64
8

304
8

312 ft2
7
240 ft2
Step 5. Area 312 ft2
8 ft2
64 ft2
8
What are the bases and height of the trapezoid?
What are the length and width of rectangle?
After we find each area what would we need to do?
3. substitute the numbers
2. substitute the formulas
1. Make a plan
Plan 3
N
trapezoid

• rectangle

F
l x w

Make a SMALL sketch of the new design.
( ) ( )
20)
(16
4
S

x 12
20
2
9
( ) ( )
20)
(16
4

x 12
20
2
( )
20)
(16
4

240
2
( )
(36)
4

4. Follow PEMDAS to solve.
240
2
144

240
2
72
240

312
10
240 ft2
Step 5. Area 312 ft2
72 ft2
11
After we find each area what would we need to do?
What is the side length of the square?
Find the radius of the circle.
1. Make a plan
2. substitute the formulas
3. substitute the numbers
What do we substitute for pi?
N
½ circle

• square

?r2
½
s2
F

(½ x x )
242
S
102
3.14
12
(½ x x )
242
102
3.14
(½ x )
242
100
3.14 x
( )
242
½ x
314
4. Follow PEMDAS to solve.
242

157
576

157
419
13
24 cm
576 cm2
Step 5. Area 419 cm2
157 cm2
2cm
2cm