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Two fractions having different denominators cannot be added or subtracted directly. They need to be converted to equivalent fractions having the same denominator to enable the addition or subtraction to take place. It is possible to use the product of the denominators of the original fractions as the common denominator but it simplifies the mathematics if the lowest common multiple of the two denominators is used.

EXAMPLE : Add 2/5 and 3/7. The lowest common denominator (also the LCM) of 5 and 7 is 35.

2/5 is equivalent to 2 x 7/5 x 7 = 14/35 : 3/7 is equivalent to 3 x 5/7 x 5 = 15/35

2/5 + 3/7 = 14/35 + 15/35 = 29/35

Q: What is the connection between the LCM and adding or subtracting fractions?

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Subtracting a fraction is the same as adding its negative.

When adding or subtracting fractions their denominators must be the same

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

Before adding or subtracting two fractions they are converted into like fractions. Explain with examples why this is necessary.

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

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What is the definition of Adding and Subtracting Like Fractions

Subtracting a fraction is the same as adding its negative.

Anything having to do with adding or subtracting unlike fractions.

When adding or subtracting fractions their denominators must be the same

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

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Before adding or subtracting two fractions they are converted into like fractions. Explain with examples why this is necessary.

Pulled and mulled

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

You need a common denominator for both.

They have to have the same denominator.

A Common Denominator