When two or more fractions have the same denominator (the number on the bottom) they have a Common Denominator.

We can add and subtract fractions only when they have a common denominator.

It is safe to multiply both top and bottom of a fraction by the same amount. Using that method we can get common denominators.

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

We can add and subtract fractions only when they have a common denominator.

It is safe to multiply both top and bottom of a fraction by the same amount. Using that method we can get common denominators.

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

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