They don't have to - it just makes calculations easier.
You don't need a common denominator to divide fractions.
The least common denominator is the least common multiple of the denominators of the fractions.
Like Fractions
Subtracting fractions is similar to adding fractions. If the fractions have the same denominator, you subtract the numerators. If the fractions have different denominators, you have to convert to a common denominator first.Subtracting fractions is similar to adding fractions. If the fractions have the same denominator, you subtract the numerators. If the fractions have different denominators, you have to convert to a common denominator first.Subtracting fractions is similar to adding fractions. If the fractions have the same denominator, you subtract the numerators. If the fractions have different denominators, you have to convert to a common denominator first.Subtracting fractions is similar to adding fractions. If the fractions have the same denominator, you subtract the numerators. If the fractions have different denominators, you have to convert to a common denominator first.
By finding the lowest common denominator of the fractions.
No only when adding or subtracting fractions a common denominator is needed
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You DO need a common denominator to add, subtract, or compare fractions. You DO NOT need a common denominator to multiply or divide fractions.
Addition or subtraction of fractions require "like" fractions: that is, fractions with the same denominator.
You Ned to find a larger common denominator or multiply the denominators to gain a common denominator.
They are called like or similar fractions.
You first convert them to similar fractions, i.e., to fractions that have the same denominator.* Step one: find a common denominator.* Step two: convert both fractions to equivalent fractions that have that denominator.