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Math for Kids23 chapters | 325 lessons

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Instructor:
*Bethany Calderwood*

Bethany has taught special education in grades PK-5 and has a master's degree in special education.

In this lesson, you will learn what circumference is, its formula and the tools you need to find circumference. Then, you can try finding the circumference of a circle on your own!

Imagine you are going for a walk around a lake, and you want to know how far you went. How would you measure the distance around the lake? The walking path around the lake is a circle. To find the distance of the walking path, you need to find the circumference of the circle. **Circumference** is the distance around the outside of a circle.

So how do we calculate the circumference of our lake? Here is the formula:

Circumference = pi x diameter

So, there are two tools me must have in order to find circumference: diameter and pi. Let's discuss these further.

**Diameter** is a straight line that goes from one side of the circle to the other and passes through the center of the circle. A line across the circle is a diameter only if it crosses the circle's center.

Look at the lake again. See the bridge that goes across the middle of the circle? Because the bridge starts on one side of the path, goes over the center of the circle, and ends at the path on the other side of the circle, that bridge is the diameter of the lake path.

**Pi** is a number that is often used in math. It is an infinite number equal to approximately 22 divided by 7, and it's usually rounded to 3.14.

Now that you know formula and tools for circumference, let's find the distance around the lake.

- The bridge across the lake is the diameter of the circle.
- The bridge is 100 yards long, so 100 yards is the diameter of the circle.
- Circumference = pi x diameter

- Replace 'pi' with 3.14 and 'diameter' with 100 yards:
- Circumference = 3.14 x 100 yards

- 3.14 x 100 yards = 314 yards
- Circumference = 314 yards

Your walk around the lake is 314 yards.

Circumference is a measurement. Measurements usually have units to tell us what the numbers are measuring. Units can be inches, feet, yards, or miles. They can also be centimeters, meters, or kilometers. The important thing when measuring circumference is to use consistent units. That means if the diameter is in yards, your circumference will also be in yards. If the diameter is in inches, the circumference will also be in inches. When you write the circumference, make sure you write the unit with the number.

Circumference is the distance around the outside of a circle, and the formula is pi multiplied by the diameter. Pi is 3.14, and the diameter is the distance across the middle of the circle from one side to the other. To find circumference, put the correct numbers into the formula and do the math, and be sure to keep your units consistent.

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13 in chapter 2 of the course:

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Math for Kids23 chapters | 325 lessons

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