Common Denominators

• A multiple is the product when you multiply a number by any other number. For example, the multiples of 5 are 5x1=5, 5x2=10, 5x3=15,etc.

• The least common multiple (LCM) is the smallest multiple that two numbers have in common

• Example: the LCM of 4 and 5 is 20 (4, 8, 12, 16, 20 and 5, 10, 15, 20)

We can use the least common multiple to find the least common denominator of two (or more) fractions. Remember, we HAVE to find common denominators before we can add or subtract fractions.

• Multiply the fractions by a WHOLE fraction (like 2/2 or 4/4 or 6/6) to change them to fractions with our common denominator without changing the value or amount. (Multiplying by 1 doesn't change the amount, right?)

• Use the new fractions with the same denominator to add or subtract the numerators!