radius & diameter
forward to
Circumference
Circumference
forward to
Area
Area
backwards to
Area
Area
Mystery Challenge
100
The length from the center of a circle to any point on the outer edge.
The radius
100
A formula for Circumference
2πr or πd
100
A formula for Area of a circle
πr2 or πrr
100
How do you get from circumference to area?
/3.14 to get the diameter
/2 to get the radius
use the area formula πr2
100
The ratio of a circles circumference to its diameter.
π or "pi"
(yes, the pi symbol is really funky on here...)
200
The largest distance across a circle, it passes through the center.
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 is it called when you multiply a number by itself?
squaring the number
200
Five Italian chefs came together to bake the world’s largest pizza. Its diameter is 131 feet long! What is the area of the pizza?
13471 ft2
200
22/7 is an over estimate for this.
3.14 is an under estimate for this.
π or "pi"
300
If my diameter is 19 inches, what is my radius?
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 28 feet across. What is the area?
615.44 ft2
300
A circular race track has a circumference of 1.57 miles. The diameter is 0.5 miles. How much area is inside the track?
0.196 miles2
(the radius was 0.25 miles)
300
If the circumference of a swimming pool is 47.1 feet, then what is the diameter? What is the radius?
15 ft. diameter
7.5 ft. radius
400
Cynthia wants to buy a round photo frame for
her brother. The radius of the photo frame is 9 cm.
What is the photo frame’s diameter?
18 cm.
400
A business has a circular lawn in front of their building. The diameter is 75 ft. How many steps would it take to walk around the entire lawn? (Round your answer to the nearest whole number)
236 steps
400
Your friend's dog is staked out in their yard on a 4.5 foot leash. How much area can the dog reach?
63.585 ft2
400
Jason's friend 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
Hilary's Horse Hideaway is buying dirt to fill their circular training area. The training circle is 28 feet across. The dirt is sold in truckloads that cover 75 square feet of ground. How many truckloads of dirt will Hilary need?
9 truckloads
500
The number of diameters it takes to make a radius.
1/2
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?
19.625 miles2
500
Mrs. Wilson placed the welcome mat shown on her front door step. What is the area of her welcome mat in square inches?
25.12 in2
(the radius was 4 in.)
(It's only half a cirlce)
500
Raise your hand, when you are called on give your teacher a compliment.
Thank you!