Instructables

Step 1: Finding the Lowest Common Denominator (LCD)

The first step of adding fractions is to find the Lowest Common Denominator (LCD). To find the LCD you must find the multiples of each of your denominators. To find a multiple you take one of you denominators and multiply it by: 1,2,3,4,etc... You then repeat this with the other denominator. The first numeral that is a multiple of both denominators is your LCD.

For this instructable we will be using a simple equation 4/5+6/15= x.
Multiples of 5 are 5, 10, 15, 20, 25,...
Multiples of 15 are 15, 30, 45,...
But wait! 15 is a multiple of both 5 and 15!

Our LCD is 15
 
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