common denominator

/ˈkɑmən dɪˈnɑməˌneɪtər/

Other forms: common denominators

In math, when two fractions have the same bottom number, they have a common denominator. You can only add or subtract fractions if they share a common denominator.

When you multiply fractions, it's easy: all you have to do is multiply the top and bottom numbers. Adding and subtracting is tricker, because that bottom number, or denominator, has to be the same in both fractions. Luckily, it's easy to give fractions common denominators. If you're adding 1/2 and 3/4, you can simply multiply that 1/2 by 2/2, which changes it to 2/4. Now the fractions you're adding have common denominators!

Definitions of common denominator

1. noun

   an integer that is a common multiple of the denominators of two or more fractions
   type of:

   denominator

   the divisor of a fraction
2. noun

   an attribute that is common to all members of a category
   type of:

   attribute

   an abstraction belonging to or characteristic of an entity