Area of circle diameter 10 cm

Step by step

The question

Question: find the area of a circle with diameter 10 cm.

1 Find the radius

The diameter goes all the way across, through the middle.

The radius goes from the middle to the edge.

It is half of the diameter.

Half of 10 is 10 divided by 2.

10 divided by 2 is 5.

So r = 5 cm.

2 Use the rule

π is a special number for circles.

It is about 3.14.

The area of a circle is π times the radius squared: A = π × r².

So we write A = π × r².

Now put the numbers in: r = 5.

5² means 5 times 5.

That is 25.

So A = π × 25.

We write it as 25π.

We keep π in the answer.

That is the exact answer.

3 About how much

To see about how much, put 3.14 for π.

25 times 3.14 is 78.5.

So the area is about 78.5 cm².

Let's look back.

First: find the radius.

Then: use the rule.

Last: about how much.