Circle Time!

Formulas

100

What are both formulas for Circumference of a circle?

C=πd

C=2πr

200

Diameter is ________ the radius.

Twice

d=2r

300

Radius is _______ the diameter.

half 

r = d/2

400

Circumference is the _______________ around a circle. 

distance 

500

What is the formula for area of a circle?

A=πr²

Radius to Diameter & Back!

100

A circle has a radius of 2, what is the diameter?

4

200

A circle has a diameter of 12, what is the radius?

6

300

The diameter is 17.5, what is the radius?

8.75

400

The radius of a circle is 34 inches, what is the diameter? (Include your units in your answer or its wrong)

68 inches

500

The diameter of a circle is 42 centimeters, what is the radius? (Include your units)

21 centimeters

Circumference

100

What is the circumference of a circle with a diameter of 10? (In terms of π)

C=10π

200

What is the circumference of a circle with a radius of 7? (In terms of π)

C=14π

300

What is the circumference of a circle with a diameter of 15 inches ? (Use 3.14 for π) (Include your units)

C = 47.1 inches

400

What is the circumference of a circle with a radius of 17.5 centimeters? (Use 3.14 for π) (Include your units)

C = 109.9 centimeters

500

If the circumference of a circle is 34.54 feet, what is the diameter? (Read it again, think about what you know, include your units)

d = 11 feet

Area

100

What is the area of a circle with a radius of 3 feet? (in terms of π) (Include your units)

A = 9π feet²

200

What is the area of a circle with a diameter of 10 centimeters? (in terms of π) (Include your units)

A = 25π centimeters²

300

What is the area of a circle with a radius of 4 inches? (Use 3.14 for π) (Include your units)

A=50.24 inches²

400

What is the area of a circle with a diameter of 15 centimeters? (Use 3.14 for π) (Include your units)

A = 176.625 centimeters²

500

A circle has a diameter of 26 units. What is the area of the circle to the nearest hundredth of a square unit?

530.66

Math Pi Facts

100

Pi day falls on this day every year.

March 14th aka 3.14

200

Is pi a rational or irrational number?

Irrational 

300

What are the first 8 digits of pi?

3.1415926

400

Pi Day, 2015 9:26am/pm is special for this reason

The first 8 digits of pi correspond to the date and time. It only happens once every 100 years. (3.1415926 = March 14, 2015 9:26)

500

Pi is approximately 3.14 but as a fraction pi is 

22/7