When two or more fractions have the same denominator (the bottom number).
We can add and subtract fractions only when they have a common denominator.
To get common denominators we can multiply both top and bottom of a fraction by the same amount.
Example: we can't add 1/3 and 1/2 as they are.
• But when we multiply 1/3 by 2/2 we get 2/6
• And when we multiply 1/2 by 3/3 we get 3/6
• Now they have a common denominator!
• We can now add 2/6 and 3/6 to get 5/6
