How to Use the LCD to Add Fractions
- 1). Multiply the denominators of the two fractions together to find a common denominator. For example, if you are adding 1/2 and 1/3, multiply 2 times 3. The result is 6, which in this case is the lowest common denominator. For larger denominators, proceed to see if you can find a smaller one.
- 2). Write out the multiples of each denominator. For example, if you are adding 1/4 and 1/6, the multiples of 4 are 8, 12, 16, etc., and the multiples of 6 are 12, 18, 24, etc.
- 3). Check your list of multiples to find the lowest number that appears on each. In this case, 12 is the lowest number on each list, so the LCD for these fractions is 12.
- 4). Divide 12 by each denominator to determine how many 12ths will be in each. Here, 12 divided by 4 is 3, and 12 divided by 6 is 2.
- 5). Multiply the numerator of each fraction (the upper number) by the corresponding number from Step 4 to get the number of 12ths in each fraction. Here, 1/4 equals 3/12, and 1/6 equals 2/12.
- 6). Add the numerators together, leaving the denominator the same to get your result. In this example, 3/12 plus 2/12 equals 5/12.
