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Fractions can only be added or subtracted if the denominators are the same.

If the denominators are different, then the fractions need to be made into equivalent fractions with the same denominator.

The new denominator can be found simply by multiplying the denominators together, but this can lead to some large fractions with which to work. A better new denominator is the lowest common multiple of (all the) denominators.

(Once the new denominator is found, the fractions' new numerators are found by multiplying their current numerator by the new denominator divided by their current denominator to make their equivalent fractions with the new denominator.)

Once all the fractions are converted into equivalent fractions with the new denominator then the fractions can be added or subtracted, with the result being simplified (if possible).

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Q: Adding and subtracting unlike denominators
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Related questions

What is the definition of adding and subtracting fractions with unlike denominators?

What is the definition of Adding and Subtracting Like Fractions

Fractions Have The Same Denominators?

Not always but they need to have the same denominators when adding or subtracting them.

How are adding fractions different?

When adding or subtracting fractions their denominators must be the same

What are the rules for adding fractions?

Ensure that the denominators are the same when adding or subtracting fractions.

What did you learn from adding and subtracting fractions?

I learned to always change the denominators before adding or subtracting the numerators. You must always have a common denominator before adding or subtracting.

How would you find the LCD when adding or subtracting rational expressions with different denominators?


Why do you have to have a common denominator?

A common denominator is needed when adding or subtracting fractions of different denominators.

What is the most important thing about adding and subtracting fractions?

Making sure the denominators are the same.

What types of problems can be solved using the the LCM?

Anything having to do with adding or subtracting unlike fractions.

How does the concept of LCM relate to fractions?

When you are adding or subtracting fractions with unlike denominators, you need to find a least common denominator, or LCD. The process is the same as finding an LCM between two integers.

Can you multiply fractions that have a different demonminator?

Yes. When multiplying and dividing fractions your denominators do not have to be the same. The denominators only haveto be the same if you are subtracting or adding them.

When adding or subtracting fractions do you have to have the numerator the same or denominator?

The denominators must be the same, the numerators can be different.