The Least Common Denominator (LCD) is the Least Common Multiple of two or more denominators.

How to find the Least Common Denominator:

• Find the Greatest Common Factor of the denominators.
• Multiply the denominators together.
• Divide the product of the denominators by the Greatest Common Factor.

Example: Find the LCD of 2/9 and 3/12

• Determine the Greatest Common Factor of 9 and 12 which is 3
• Either multiply the denominators and divide by the GCF (9*12=108, 108/3=36)
• OR - Divide one of the denominators by the GCF and multiply the quotient times the other denominator (9/3=3, 3*12=36)

How to rename fractions and use the Least Common Denominator:

• Divide the LCD by one denominator.
• Multiply the numerator times this quotient.
• Repeat the process for the other fraction(s)

Example: Add 2/9 + 3/12

• LCD is 36
• First fraction (2/9): 36/9 = 4, 4*2 = 8, first fraction is renamed as 8/36
• Second fraction (3/12): 36/12 = 3, 3*3 = 9, second fraction is renamed as 9/36
• It is possible to add or subtract fractions that have the same denominator
• 8/36 + 9/36 = 17/36