Uncommon Denominators
To add or subtract fractions with uncommon denominators, first find the least common denominator (LCD), then adjust each fraction accordingly. Add or subtract numerators and keep the denominator constant. Finally, simplify if possible.
Fractions have uncommon denominators when their denominators, the numbers below the fraction line, are different from each other.
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To find the least common multiple (LCM) of two or more numbers, list the multiples of each number until you find a common multiple. Then, select the smallest common multiple.
Least common multiple
To cross-multiply fractions, you multiply the numerator of one fraction by the denominator of the other fraction, and vice versa. For example, to compare a/b and c/d, you cross multiply to get a x d and c x b. Then you can compare the results to determine the relationship between the fractions.
This technique is commonly used when adding or subtracting fractions with unlike denominators, where you need to find a common denominator.
