6th Grade

SPI: 0606.4.4 Calculate with circumferences and areas of circles.

The circumference of a circle is

The distance around a circle

Hint: Circumference remember circle around

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!

The diameter is the distance across a circle through the

center.

We use Pi as the measurement to help us find the circumference of a circle.

Pi, not Pie!

HINT: Pi =3.14

Two formulas are used in finding the circumference of a

circle.

Circumference = d 3.14 x 4in.

12.6in.

WHEN THE CIRCLE HAS A DIAMETER MEASUREMENT, USE THE FOLLOWING FORMULA.

4in.

Circumference = 2 r

When the radius of a circle is given, the following formula

should be used.

2 x 3.14 x 5cm

31.4cm

HINT: Always round your answers to the

nearest tenth.

NOW…Let’s have some fun.

Tell me what formula would be used to solve the next five problems.

3in

C = 2 x 3.14 x r

8ft

C = 3.14 d

122mm

C = 2 x 3.14 x d

17.5 cm

C = 3.14 x d

122.5mm

C = 2 x 3.14 x r

Now that we have determined the correct

formula for each, let’s work the problems.

3in

C = 2 x 3.14 x r

The answer is: 18.8in

8ft

C = 3.14 d

The answer is: 25.1ft

122mm

C = 2 x 3.14 x d

The answer is: 766.2mm

17.5 cm

C = 3.14 x d

The answer is: 55cm

122.5mm

C = 2 x 3.14 x r

The answer is: 76,930mm