Circumference Bell Ringers
1. A pair of jeans cost 12.99 to make. If Old Navy marks
up the jeans by 45%, what will be the cost of the jeans.
2. Bobby makes a 8% commission on a house that sold
for 250,000. How much will he make in commission.
3. A computer is on sale for 120.99 after a 20% discount.
What is the original price of the computer.
4. I go out to lunch and buy a sandwich for 6.99, drink for
1.25, and a cookie for .99. If sales tax is 9% and I leave
a 20% tip what will my total bill be?
Created By: Melissa Forsyth
7.G.4 Circumference of a
Circle
Created By: Melissa Forsyth
Circles
• A circle is the set of all points in a plane that are
the same distance from a given point, called the
center.
Created By: Melissa Forsyth
Circles
The diameter (d) is
the distance across a
circle through the
center of the circle.
The circumference
(C) is the distance
around a circle.
The area (A)
is the amount
of twodimensional
space taken
up by an
object.
Created By: Melissa Forsyth
The radius (r) is the
distance from the
center to any point on
the circle.
Circles
• Pi is a non-terminating and non-repeating
number represented by the Greek letter
•  (pi)
• 3.14 is often used as an approximation for
.
Created By: Melissa Forsyth
To Find Area of a Circle
The Area (A) of a Circle is found by using the following
formula:
Squared or to the second
power: radius x radius
Radius: The
distance from the
center to the edge
of a circle
A = Area
It is half of the
circle's diameter.
Created By: Melissa Forsyth
Circles - Area
• Formula for finding the area of a circle:
2
• A = r
• If you are given the diameter instead of the
radius; divide the diameter by 2 to get the
radius.
Created By: Melissa Forsyth
Calculate the area of the
following circle
Area = π r2
First, you must find half of your
diameter: 2 ÷ 2 = 1
A = π 12
A=π1x1
A = 3.14 x 1
A = 3.14 yd2
Created By: Melissa Forsyth
Calculate the area of the
following circle
Area = π r2
A = π 52
A=π5x5
A = 3.14 x 25
A = 78.5 km2
Created By: Melissa Forsyth
Calculate the area of the
following circle
What is the area of a circle with a diameter
of 5 meters?
Area = π r2
First, you must find half of your
diameter: 5 ÷ 2 = 2.5
A = π 2.52
A = π 2.5 x 2.5
A = 3.14 x 6.25
A = 19.625 m2
Created By: Melissa Forsyth
Calculate the area of the
following circle
A clock’s minute hand is 7.0 inches long.
How much area it sweeps in 1 hour?
Area = π r2
A = π 7.02
A=π7x7
A = 3.14 x 49
A = 153.86 in2
Created By: Melissa Forsyth
Calculate the area of the
following circle
A circular linen tablecloth has a diameter of
70 inches. How many square inches of
linen was required to make this tablecloth?
Area = π r2
First find the radius by dividing the
diameter in half: 70÷ 2 =35
A = π 352
A = π 35 x 35
A = 3.14 x 1225
A = 3846.5 in2
Created By: Melissa Forsyth
Calculate the area of the
following circle
A sheep is tied to a post in the field. If the
length of the rope is 45 feet, what is the area
of the field in which the sheep can graze?
Area = π r2
A = π 452
A = π 45 x 45
A = 3.14 x 2025
A = 6358.5 ft2
Created By: Melissa Forsyth
Finding a Circle’s Circumference
•
•
•
•
Formulas for finding Circumference
C = d
C = 2r
If you are given the diameter in a problem
use the formula with d. If you are given a
problem with the radius use the formula
with r.
• Both formulas find the circumference.
Created By: Melissa Forsyth
Find Circumference
C = 2r
21 in
C = 2(21)
C = 2 x 3.14 x 21
C = 131.88 inches
Created By: Melissa Forsyth
Your Turn
Find the Circumference
C = d
C = (4.5)
4.5cm
C = 3.14 x 4.5
C = 14.13cm
Created By: Melissa Forsyth
How are Circumference and Area Related
How can we find circumference given the area.
A= 113.04 in2
Think of the formulas:
A= π r2
C=2 πr
What do both formulas have in common?
The radius.
113.04 = π r2
113.04 = 3.14 r2
113.04
3.14
=
3.14r2
3.14
36 = r2 (To find the opposite of squared you need to
find the square root. √)
√36 = √r2
r=6
C= 2 π r
C=2π6
C = 2 x 3.14 x 6 = 37.68 in
Created By: Melissa Forsyth
Calculate the circumference of the following
circle.
A = 153.86 ft2
Created By: Melissa Forsyth
Calculate the circumference of the following
circle.
A = 12.56 yd2
Created By: Melissa Forsyth
How are Circumference and Area Related
C = 56.52 in
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Calculate the area of the following circle.
C = 508.68 yd
Created By: Melissa Forsyth
Calculate the area of the following circle.
C = 62.8 yd
Created By: Melissa Forsyth