Finding Radius & Diameter (Using Circumference)
Finding Circumference
Finding Area (Using R & D)
Finding Area (Using Circumference)
Miscellaneous
100
The length from the center of a circle to a side (or rim)
The radius
100
What are 2 formulas used to find Circumference?
2πr or πd
100
A formula for Area of a circle
πr2 or πrr
100
What's wrong with this formula for area of a circle?
pi • radius • 2
It isn't radius•2, you must use radius2
100
We find this when solving Circumference ÷ Diameter
π or "pi"
(yes, the pi symbol is really funky on here...)
200
A line that goes from side to side while passing through the center of a circle is called what?
The Diameter
200
The Jones family wants to enclose their circular garden with a fence. The radius is 62.5 ft. What is the minimum length of fencing they need to buy?
392.5 ft.
200
What should I do first when given the diameter and told to find the area?
Divide by 2 to find the radius, then use the area formula
200
Five Italian chefs came together to bake the world’s largest pizza. Its radius is 60.5 feet long! What is the area of the pizza?
11493.185 ft2
200
What 3 digits do we use for pi?
3.14
300
If my circumference is 29.83 inches, what is my diameter?
9.5 in.
300
A bicycle tire has a diameter of 20 inches. How many inches is one full revolution of the wheel?
62.8 in
300
Hilary's Horse Hideaway is buying dirt to fill their circular training area. The training circle is 14 feet from the center pole to the fence. What is the area?
615.44 ft2
300
A circular race track has a circumference of 1.57 miles. How much area is inside the track?
0.19625 miles2
(the radius was 0.25 miles)
300
What are the steps to go from Circumference to Radius?
Divide by 3.14 then divide by 2
400
Cynthia wants to buy a round photo frame for
her brother. The circumference is 56.52 cm. What is the radius?
9 cm.
400
A business has a circular lawn in front of their building and want to put a fence around it. The diameter is 75 ft. How much fencing would it take to go around the entire lawn?
235.5 ft
400
A stereo speaker measures 9 inches from side to side. What is the area this speaker covers?
63.585 in2
400
Fred is painting a large circle on one wall of his new apartment. The circumference of the circle will be 25.12 feet. Approximately how many square feet of wall will the circle cover?
50.24 ft2
(the diameter was 8)
(the radius was 4)
400
What's wrong with this formula for finding area of a circle:
pi² • radius
The ² should be on the radius, not pi
pi • radius²
500
A Texas size doughnut measures 38.465 inches around. What is the diameter & radius of the doughnut?
Diameter = 12.25
Radius = 6.125
500
A circular race track has a diameter of 1/2 mile.
How far does a car travel in one lap around the
track?
1.57 miles
500
What is the area of the yellow part of the circle?
52 x 3.14 = 78.5
78.5 ÷ 4 = 19.625 miles2
500
Mrs. Wilson placed a welcome mat on her front door step that measured 86.35 inches around. What is the area of her welcome mat in square inches?
diameter = 27.5 in
radius = 13.75 in
area = 593.65625 in2
500
How do you go from circumference to area?
Divide by 3.14 to get diameter
then divide by 2 to get radius
then pi • radius²