NAME ____________________________________________ DATE _____________________________ PERIOD _____________
Practice 7.8(C)
SCORE __________
Use models to determine the approximate formulas for the circumference and area of a circle and connect the models to
the actual formulas.
Multi-Step Example
David is painting two circles on his bedroom wall. The red circle has a radius of 5 inches and the blue
circle has a radius of 18 inches. How much more of the wall will be covered with the blue circle than
the red circle?
Draw the red and blue circles.
If the circles are cut and reassembled, the sections
form a parallelogram.
You can show that the length of the parallelograms is half the circumference of the corresponding circles.
Red Circle
Blue Circle
𝟏
𝟏
𝟐
C=
≈
𝟏
𝟐
𝟏
𝟐
• 2πr
𝟐
C=
• 2 • 3 • 14 • 5
≈
≈ 15.7
𝟏
𝟐
𝟏
𝟐
• 2πr
• 2 • 3 • 14 • 18
≈ 56.52
Therefore, the areas of the circles are the same as the areas of the corresponding parallelograms.
Red Circle
A = π𝑟
≈ 3.14(5)
≈ 78.5
Blue Circle
Rectangle
!
A = π𝑟
A = bh
!
!
Rectangle
A = bh
= 15.7 • 5
≈ 3.14(5)!
= 56.52 • 18
= 78.5
≈ 1,017.36
= 1,017.36
So, the blue circle covers 1,017.36 – 78.5 or 938.86 more square inches than the red circle.
= 1,017.36
1 Jenny’s bicycle tires have a radius of 8.2 inches.
Approximately how much rubber goes around the
outside of both tires? Use 3.14 for π.
2 The Westside Dog Kennel is building a circular dog
park. The length of the fence around the park is
approximately 110 feet. How much area will the dogs
have to run? Use 3.14 for π.
A 26 in.
F 55 ft !
B 52 in.
C 72 in.
G 963 ft !
D 103 in.
H 1,175.5ft !
J 3,853.5 ft !
Course 2 • Expressions, Equations, and Relationships TX93 NAME ____________________________________________ DATE _____________________________ PERIOD _____________
Practice 7.8(C)
(continued)
SCORE __________
3 The manager at Adventure Park is painting the sun dial
shown at the entrance of the park. The sun dial has a
radius length of 10 feet. Each section of the sun dial
will be painted in different colors. Approximately how
much paint is needed for one section? Use 3.14 for π.
6 Dirk ordered a circular pizza that was 16 inches wide.
If Dirk ate a quarter of the pizza, how many square
inches of the pizza did he eat? Use 3.14 for π. Round
to the nearest hundredth.
Record your answer and fill in the bubbles on your
answer document. Be sure to use the correct place
value.
7 Linda is making a mosaic stepping stone to place in
her garden. The stone is shown below. How much
mosaic glass tile will Linda need to cover the surface
of five stepping stones? Use 3.14 for π.
A 52.3 ft !
B 78.5 ft !
C 209.3 ft !
A 56.52 in!
D 314 ft !
4 Jackson is riding a Ferris wheel at a carnival that has a
diameter of 49 feet. What distance does Jackson travel
!!
in three revolutions on the Ferris wheel? Use for π.
!
Record your answer and fill in the bubbles on your
answer document. Be sure to use the correct place
value.
5 The manager at Fortress Golf Course wants to reseed
the fairways. The manager will only put seed where
the sprinklers water the grass. If one sprinkler sprays a
diameter of 12 feet, approximately how much ground
will be covered with seed? Use 3.14 for π.
B 113.04 in!
C 282.6 in!
D 565.2 in!
8 Rose has a circular trampoline in her backyard. The
center of the trampoline is the area Rose has to jump,
which is approximately 22 square feet. The length of
each spring that attaches the center of the trampoline
to the outer bar of the trampoline is 3 inches long.
What is the length of the outer edge of the trampoline?
Use 3.14 for π.
F 6 ft !
G 113 ft !
H 216 ft !
J 452 ft !
F 2.7 ft
G 5.8 ft
H 18.2 ft
J 100.2 ft
TX94
Course 2 • Expressions, Equations, and Relationships
NAME ____________________________________________ DATE _____________________________ PERIOD _____________
Practice 7.8(C)
SCORE __________
Student Recording Sheet
Fill in the correct answer. For gridded-response questions, write your answers in the boxes on the answer grid and
fill in the bubbles to match your answers.
1
2
3
5 6
4
7
Course 2 • Expressions, Equations, and Relationships
8
TX95