Common denominator

Definition

A denominator shared by two or more fractions so that they can be added or subtracted.

Used by AQA and OCR

Specification N8 · Paper 1, Paper 2, Paper 3

Fractions can be added or subtracted directly only when they describe parts of the same size—that is, when they have a common denominator.
Revise: Exact Calculations with Fractions

Specification 2.04a, 6.01g · Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Foundation), Paper 4 (Higher), Paper 5 (Higher), Paper 6 (Higher)

A fraction whose denominator is shared by one or more other fractions, allowing their numerators to be compared directly.

1
For addition or subtraction, obtain a common denominator before combining the numerators. Do not add or subtract the denominators.

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If all the values are fractions, you can use a common denominator instead of decimals.

A denominator shared by two or more fractions, used when adding or subtracting them.