- 1). When adding fractions with different denominators, which are the numbers on the bottom half of the fraction, a common denominator is imperative to do the job.Find the lowest common denominator by listing the multiples of each denominator. For example when trying to solve the equation1/3 + 2/4 = ?
- 2). Three and four are different denominators and can’t be added together, therefore a common denominator must be found. Start by listing the multiples of three and four. Some of the multiples of three are: 3, 6, 9, 12, 15, 18, 21 Some of the multiples of four are: 4, 8, 12, 16, 20, 24, 28
- 3). Comparing the two lists of multiples, the number 12 is the lowest number in both lists. It will be used as the lowest common denominator. When using the lowest common denominator, it has to be remembered that whatever is done to the denominator has to be done to the numerator. So, when changing the denominator in the fraction 1/3 the three is multiplied by four to get twelve. Since the three is multiplied by four then the one also has to be multiplied by four. 1/3 = 4/12
- 4). Repeat these steps for the fraction 2/4. The four is multiplied by three to get twelve so the two also has to be multiplied by three. 2/4 = 6/12
- 5). Add the two new fractions together by adding the numerators and leaving the denominators as twelve. 4/12 + 6/12 = 10/12
- 6). Take the 10/12 and reduce it by dividing by a common factor. In this case the common factor would be two. 10/12 = 5/6
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