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So that you can get the correct answer. Add one half and one third. What do you get? But if you know that 1/2 = 3/6 and 1/3 = 2/6, then you know the answer is 5/6 which is probably not what you got when you added 1/2 + 1/3 without converting them.

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7y ago
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5y ago

It will help you to get the right answer. Just by looking at it, what do you think 1/2 + 1/3 is? If you realize that 1/2 is equal to 3/6 and 1/3 is equal to 2/6, then 5/6 is the obvious correct answer.

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7y ago

This follows from the way in which addition and multiplication are defined. Addition requires like terms, multiplication does not. Incidentally, "like terms" are also required for adding algebraic terms but not for multiplying.

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5y ago

You do not "make" a common denominator. It is a consequence of the way in which numbers and multiplication are defined. A common denominator of a set of numbers is any number which can be evenly divided (divided without remainder) by every member of the set.

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Q: Why do fractions need a common denominator before add or subtract them?
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Find the LCD then add or subtract?

To add or subtract fractions the denominators must be the same - then the numerators are added or subtracted with the denominator being kept the same.When adding or subtracting fractions with different denominators, the fractions must first be converted into equivalent fractions with the same denominator and then the (new) numerators can be added or subtracted as required.For the denominator for these equivalent fractions, the original denominators can all be multiplied together, but this can lead to having to work with very large numbers; a better choice for the denominator is the smallest number that all the denominators divide into, their Least Common Multiple (LCM) - this is is then used as the denominator for the equivalent fractions and is called the Least Common Denominator (LCD) of the fractions.First you find the LCD okay??? Then you have to add or subtract. What they mean by that is that once you've found your lcd add or subtract..xx hope i helped :)


Why do fractions need a common denominator when adding subtracting?

In order to add or subtract one fraction from another, they must have a common denominator, or the same denominator. That's because it's impossible to add two fractions that have a different number of parts.


How can the greatest common factor and least common multiple help you work with fractions?

Finding the GCF of the numerator and the denominator of a fraction and dividing them both by it will give you the simplest form of that fraction. Finding the LCM of unlike denominators and converting them to it will make it possible to add and subtract unlike fractions.


What does it mean to get a common denominator?

Sometimes fractions have different denominators, like 2/3 and 3/4. If you want to add or subtract them, they need to have the same denominator. In order to do that, you find a common denominator which is the same thing as a common multiple, only with denominators.


Why might it be important to know to calculate least common multiples?

The process of finding the LCM is the same as finding the least common denominator which is important when you want to add and subtract fractions.

Related questions

Do you need a common denominator for all fractions before doing the order of operations?

You DO need a common denominator to add, subtract, or compare fractions. You DO NOT need a common denominator to multiply or divide fractions.


How do you minnous 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.


How do you subtract fractions when denominator is different?

By finding the lowest common denominator of the fractions.


How do subtract two fractions with different denominator?

First find the lowest common denominator and then adjust the fractions accordingly before subtracting the numerators


When do you need a common denominator?

The denominators must be the same before you can add or subtract fractions.


Why do fractions need a common denominator before you add or subtract?

Because the answers will be wrong when adding or subtracting them if they don't have a common denominator.


How do you subtract fractions in simplest form?

You first need to find a common denominator, not necessarily the least common denominator. Next, you rename the fractions according to the common denominator. Only then can you subtract the fractions. After subtraction you should simplify the answer.


Why do you need a common denominator?

Common Denominator means that the denominators in two (or more) fractions are common, or the same. The common denominator is important because before you can add or subtract fractions, the fractions need to have a common denominator.Sometimes fractions have different denominators, like 2/3 and 3/4. If you want to add or subtract them, they need to have the same denominator. In order to do that, you find a common denominator which is the same thing as a common multiple, only with denominators.


What you need to add or subtract fractions?

You need a common denominator in order to add or subtract fractions.


How do you subtract fractions with unequal denominators?

by finding the common denominator of the fractions


Do you have to find a common denominator to subtract fractions?

Yes.


How do you add or subtract dissimilar 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.