Least Common Multiple (LCM) Used to find the Least Common Denominator (LCD) Example: Find the LCM of 30 and 45 Note: There are four common methods; DO NOT mix the steps of the methods! 

Method 1


Method 2


Method 3


Method 4

In each exercise, find the LCM of the given numbers.
1) 4 and 18
2) 16 and 40
3) 20 and 28
4) 5 and 8
5) 12 and 18
6) 12 and 16
7) 50 and 75
8) 24 and 30
9) 36 and 45
10) 8 and 20
11) 16 and 20
12) 28, 35, and 21
Addition and Subtraction of Fractions with the Same Denominator To add or subtract fractions, the denominators MUST be the same. 

Example 1:


Example 2:

Add or Subtract as indicated.
Addition and Subtraction of Fractions with Different Denominators Remember: In order to add or subtract fractions, the denominators MUST be the same. Example:

Add or Subtract:
Subtraction of Fractions with
Borrowing
Note: There are two common methods; DO NOT mix the steps of the methods! 

Method 1 Example 1

Subtraction with Borrowing  
Write problem vertically Cannot subtract fraction from whole without finding common denominator. 

Borrow one whole from 7 and express as  
Subtract numerators and whole numbers.  
Example 2


Write problem vertically and find LCD Cannot subtract 5 from 2. 

Borrow one whole from 5,and add  
Subtract numerators and whole numbers; reduce as needed. 

Method 2 Example 1:

Subtraction Using Improper Fractions Write the problem vertically. 

Convert the whole numbers and mixed numbers to improper fractions using the LCD. 

Subtract
and convert improper fraction to mixed number. 

Example 2:

Write problem vertically and find the LCD.  
Change the mixed numbers to improper fractions.  
Subtract the numerators. Convert to a mixed number. 

Reduce. 