4.5 Subtracting Fractions 
Mme DiMarco
Learning Goal
 Learning Goal: Subtract fractions using symbols and
algebra
To Review…
To add fractions…
1. Find the LCM of the two denominators
2. Change the two fractions to equivalent fractions
using the LCM as the denominator
3. Add the numerators together over the LCM as the
denominator
4. Simplify the fraction
Subtracting Fractions
 To subtract fractions, we use the same steps that we
would to add them, with one difference…
 Instead of adding the denominators, we subtact them 
To Subtract Fractions
 Step 1: find the common denominator of the two fractions (LCM)
¾-⅙=x
LCM of the two denominators:
4: 4, 8, 12, 16, 20, 24…
6: 6, 12, 18, 24, 30…
Therefore, the new equation will have denominators of 12.
To Subtract Fractions
 Step 2: Transform the equation into equivalent
fractions using the common denominator found in
step 1.
¾ - ⅙ = x  9/12 – 2/12 = x
To Subtract Fractions
 Step 3: subtract the two numerators
9/12 – 2/12 = 7/12
To Subtract Fractions
 Step 4: Reduce the fraction to its simplest form.
7/12
Since 7 and 12 have no common factors other than 1, we
cannot simplify this fraction any further!
Mixed Numbers and Improper Fractions
Mixed Number  Improper Fraction
Improper Fraction  Mixed Number
1. Multiply the whole number by the
denominator
1. Divide the numerator by the
denominator
1. Add the product from Step 1 to the
numerator
1. Write the whole number
1. Write the sum on the denominator
Example : 1 ¾  7/4
1. Write the remainder on top of the
denominator
Example: 11/4  2 ¾
Homework 
 Page 137, questions 1 - 6, 8 and 9