Who invented the round table?

Sir Cumference!

The **circumference **of a circle simply means the **distance around the circle**. It can also be called the **perimeter** of the circle.

There are a few other things you need to know:

**Diameter**

The diameter is the line that cuts through the centre of the circle.

**Radius**

The **radius **comes from the centre of the circle to the edge and is** half the diameter.**

**Pi**

No, not that pie, this one:

You will need to learn the value for this..sorry. Did you know that pi is infinite - some people can quote it to hundreds of decimal places?

Lucky for you that you only need to use it to 3 decimal places, which is **3.142**

Finally, you need **the formula **for finding the circumference of a circle:

**Circumference of a circle = pi x diameter **or **C = pi x d**

A great way to remember it is Cherry Pies are delicious!

Building a toolbox is useful. Builders have them, and so do mathematicians as we are building our knowledge.

Our toolbox contains definitions for circumference, perimeter, diameter, radius, pi and the formula.

Let's get started.

Calculate the circumference of this circle.

** Pi x diameter**

**3.142 x 14 = 43.988 cm ** (43.99 cm to 2 decimal places)

You will be asked to round to decimal places or significant figures.

Warning!

You might get a question that gives you the **radius.**

Remember that the radius is only half of the diameter, so **double** it first.

Calculate the circumference of a circle with a radius of 3 cm.

3 + 3 = 6 cm diameter

Now apply the formula: **Pi x diameter**

3.142 x 6 = 18.852 (18.9 to 3 significant figures)

**You can use the pi button on your calculator for many calculations, but for this activity take the value of pi to be 3.142**