In this section, a proportion is used to find the arc length. A calculator is needed.

A proportion written in the form Part 1 Whole 1 = Part 2 Whole 2 can be used to find the length of an arc. Part 1 and Whole 1 are usually what we know. Part 2 and Whole 2 include one unknown piece of information.

Example: Use the information obtained in section one to find the arc length of the blue M&Ms on the circle.

Below is a chart with the information obtained in section 1.

 Color Number Fraction of Total Red 6 6 25 Blue 5 5 25 = 1 5 Green 6 6 25 Yellow 4 4 25 Brown 4 4 25 Total 25 25 25 = 1

Part 1 is the number of a certain color (blue) of M&Ms and Whole 1 is the total number of M&Ms.

Part 1 Whole 1 = Number of a certain color of M&M All the M&Ms

The variable, or information that we don't know, is part of the second fraction: Part 2 Whole 2

Three out of the four pieces of information must be known in order to solve a proportion.

Fill in the following. Use the variable x or y for unknown values. Click on the blanks to reveal the answers.

A general equation to find the length of an arc is:

Degree measure of the sector360° in a circle = Measure of arc length Circumference of circle

Example: Given the circle below, find the arc length of the shaded part of arc AB.

Check logically:

Another Example