How to find Circumference

Question

I don't get how to find circumference with fractions

Answer 1

Hi Bob,

You're asking how to find circumference of a circle when using fractions. I'm going to assume that means that the radius of your circle is a fraction.

Let's look at the formula for circumference:

C = 2πr

I can show an example using a circle with the radius 2/5 in.

C = 2π × 2/5

If we multiply 2 × 2/5, we get 4/5. Some teachers may accept your answer in the format C = 4/5in.× π .

However, you may be asked to round to the nearest hundredth (or another decimal place) in your answer. In this case, you need to convert your fraction to a decimal.

4/5 = 0.8

C = 0.8in.× π ≈ 0.8in × 3.14

C=2.512 in.

If we round to the nearest hundredth in our answer, we would write the following: The circumference of the circle is 2.51 in.

You can also use a fraction approximation for pi. You would substitute the fraction 22/7 for pi in the equation C = 2πr. We would find the circumference of our circle with the 2/5 in radius as follows:

C = 2(22/7) × 2/5

C = 44/7 × 2/5

C = 88/35

C=2-18/35 in.

Good luck with your math studying! if this answer was helpful, give it a thumbs up.