To add or subtract fractions the denominator must be the same. Find the lowest common multiple (LCM) of both denominators.
The LCM is the lowest number that is in both of the times tables of the denominators.
Multiply both denominators by whatever number is needed to make them into the LCM. (You may have to only multiply one of the denominators). For example if the denominators are 4 and 12 the LCM is 12. Multiply the 4 by 3 to make it 12. The 12 can be left alone.
Muliply the numerator of each fraction by the number you multiplied its denominator by.
Now that both fractions have the same denominator, add or subtract just the numerators. Do not add or subtract the denominators. The answer will have the same denominator as the fractions you added or subtracted.
1⁄4 + 3⁄12
The LCM of 4 and 12 is 12. (3 X 4 = 12, 1 X 12 = 12) You only need to multiply the left hand fraction.
3⁄12 + 3⁄12 = 6⁄12
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