4.5 Subtracting Fractions Mme DiMarco

Learning Goal: Subtract fractions using symbols and algebra

Learning Goal

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

To Review…

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

Subtracting 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!

To Subtract Fractions

Mixed Number Improper Fraction

Improper Fraction Mixed Number

1. Multiply the whole number by the denominator

2. Add the product from Step 1 to the numerator

3. Write the sum on the denominator

Example : 1 ¾ 7/4

1. Divide the numerator by the denominator

2. Write the whole number

3. Write the remainder on top of the denominator

Example: 11/4 2 ¾

Mixed Numbers and Improper Fractions

Page 137, questions 1 - 6, 8 and 9

Homework