1. SPI: 0606.4.4 Calculate with circumferences and areas of circles.
6th Grade
SPI: Calculate with circumferences and areas of circles.

2. The circumference of a circle is
The distance around a circle
Hint: Circumference remember circle around

3. First we must define some things about a circle.
The radius is the distance from the center of a circle to any point on a circle.
Hint: I like to define it as halfway through!

4. The diameter is the distance across a circle through the center.

5. We use Pi as the measurement to help us find the circumference of a circle.
Pi, not Pie!

6. HINT: Pi =3.14

7. Two formulas are used in finding the circumference of a circle.
WHEN THE CIRCLE HAS A DIAMETER MEASUREMENT, USE THE FOLLOWING FORMULA.
Circumference = d
4in.
3.14 x 4in.
12.6in.

8. HINT: Always round your answers to the nearest tenth.
When the radius of a circle is given, the following formula should be used.
Circumference = 2 r
2 x 3.14 x 5cm
31.4cm
HINT: Always round your answers to the nearest tenth.

9. Tell me what formula would be used to solve the next five problems.
NOW…Let’s have some fun.
Tell me what formula would be used to solve the next five problems.

10. 3in
C = 2 x 3.14 x r

11. 8ft
C = 3.14 d

12. 122mm
C = 2 x 3.14 x d

13. 17.5 cm
C = 3.14 x d

14. 122.5mm
C = 2 x 3.14 x r

15. Now that we have determined the correct formula for each, let’s work the problems.

16. The answer is: 18.8in
3in
C = 2 x 3.14 x r

17. 8ft
C = 3.14 d
The answer is: 25.1ft

18. 122mm
C = 2 x 3.14 x d
The answer is: mm

19. 17.5 cm
C = 3.14 x d
The answer is: 55cm

20. 122.5mm
C = 2 x 3.14 x r
The answer is: 76,930mm