Ok. First you make sure the denominator (bottom number) is the same on all the fractions. The easiest way to do this is to multiply the denominators together, then multiply each numerator by the opposite fractions denominator. This is the easiest way to do this, you will simplify later. ONLY DO THIS IF THE DENOMINATORS ARE DIFFERENT. If they are the same just add the numerators together to get your fraction. Then simplify.
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If the denominators are not the same, then you have to use equivalent fractions which do have a common denominator . To do this, you need to find the least common multiple (LCM) of the two denominators. To add fractions with unlike denominators, rename the fractions with a common denominator.
The Least (or Lowest) Common Multiple (LCM) is the smallest number that is a multiple of both numbers. For example: the LCM of 10 and 4 is 20, because both 10 and 4 go into 20 and 20 is the smallest number both 10 and 4 can go into. To be able to add or subtract fractions they must have the same denominator. If the denominators are different then the fractions must first be converted into equivalent fractions with a common denominator; any common denominator can be used, but by using the Least Common Multiple of the denominators as the new denominator it keeps the numbers smaller; this smallest denominator is known as the Least Common Denominator Thus the Least Common Denominator is the Least Common Multiple of the denominators of two (or more) fractions (used when adding or subtracting fractions with different denominators). As the Least Common Multiple is used most often with adding or subtracting fractions, it is often referred to as the Least Common Denominator (because the numbers being considered are usually denominators of fractions).
You convert them to equivalent fractions with the a common denominator. This new denominator must be a common multiple of the denominators. The Least Common Multiple (LCM) may be a recommendation but is not necessary. However, using the LCM will keep all the numbers as small as possible and that may be an advantage.
Using the Euclidean algorithm
Adding or subtracting fractions requires the use of a common multiple. It is rare that the LEAST common multiple is required - it is useful to keep the numbers small and manageable.