To Subtract Fractions with different denominators:
- Find the Lowest Common Denominator (LCD) of the fractions
- Rename the fractions to have the LCD
- Subtract the numerators of the fractions
- The difference will be the numerator and the LCD will be the denominator of the
answer.
- Simplify the Fraction
Example: Find the difference between 3/12 and 2/9.
- Determine the Greatest Common Factor of 12 and 9 which is 3
- Either multiply the numbers and divide by the GCF (9*12=108, 108/3=36)
- OR - Divide one of the numbers by the GCF and multiply the answer times the other
number (12/3=4, 9*4=36)
- Rename the fractions to use the Lowest Common Denominator (3/12=9/36, 2/9=8/36)
- The result is 9/36 - 8/36
- Subtract the numerators and put the difference over the LCD = 1/36
- Simplify the fraction if possible. In this case it is not possible