How to Find the Perimeter With Fractions

You should have strong multiplication skills before you attempt to add or subtract fractions.

To find the perimeter of any shape or object, you must add its side lengths. For example, to calculate the perimeter of a square, you would find the length of one side and multiply it by four. To find the perimeter of a triangle, you will combine the lengths of its three sides. While integers are simpler to add up, you can also find the perimeter of any shape measured in fractions by finding their common denominator.

Things You'll Need

• Pencil
• Paper

Instructions

1. Set up the equation. Try this problem: Find the perimeter of a rectangle whose length is 1/4 inch and whose width is 5/3 inch. You know that a rectangle has two pairs of equal sides, so the equation is: 1/4 + 1/4 + 5/3 + 5/3 = perimeter.

2. Find the lowest common denominator of the fractions. The common denominator is a multiple of the both numbers. The lowest common denominator for 4 and 3 is 12.

3. Multiply the denominators of each fraction with the number that, when multiplied to the denominator, equals the lowest common denominator. Multiply the numerator by the same number. 1(3)/4(3) + 1(3)/4(3) + 5(4)/3(4) + 5(4)/3(4).

4. Simplify the equation: 3/12+3/12+20/12+20/12. Now that you have all the same denominator, you can total up the numerators: 46/12. Reduce the fraction: 23/6. You can also convert to a decimal: 3.833.

References

• Math is Fun: Adding Fractions