Finding a common denominator makes it possible to add two fractions because it allows us to write each fraction as a multiple of a common (usually smaller) fraction.
Subtracting fractions works the same way; find a common denominator so that the fractions involved are in the same terms.
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You cannot add or subtract fractions with different denominators. If the denominators are different then you need to work with equivalent fractions.
You need common denominators. Then add or subtract the numerators. If the answer is an improper fraction it is common practice to reduce it to a mixed number.
Because if you skip that step . . . -- you'll need to invent your own method for adding fractions with different denominators, because every method you'll ever be taught or find on your own requires common denominators, and -- the answer you get will be wrong.
Yes. You need common denominators if you want to:Add fractionsSubtract fractionsCompare fractions ("which is larger?")You do not need common denominators to multiply or divide fractions. Thus, in the case of fractions, multiplication and division is actually easier than addition and subtraction.
Answer: When adding or subtracting fractions with different denominators it is important to change the denominators into the lowest common denominator by using equivalent fractions. Answer: Equivalent fractions are used to: * Simplify fractions. It is sort of inelegant to write the final solution of a problem as 123/246, when you can just as well write it as 1/2. * Add fractions. If two fractions have different denominators, you need to convert them to equivalent fractions that have the same denominator. Only then can you add. * Subtract fractions (same as addition). * Compare fractions, to check which one is larger (same as addition).