In order to add and subtract fractions with unlike denominators, it is necessary to convert them to equivalent fractions with a common denominator.
Example: 1/4 + 1/6
The LCM of 4 and 6 is 12.
1/4 = 3/12
1/6 = 2/12
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The least common denominator is the least common multiple of the denominators of the fractions.
Find the equivalent fractions with the same denominator (the least common multiple) and then compare the numerators.
First you find a common multiple of the denominators. The least common denominator is handy but not essential. This number will be the denominator of the answer - before simplification.For both fractions find an equivalent fraction whose denominator is this common denominator.Carry out the subtraction on the new numerators to give the numerator of the answer.Simplify the result for the final, simplified answer.First you find a common multiple of the denominators. The least common denominator is handy but not essential. This number will be the denominator of the answer - before simplification.For both fractions find an equivalent fraction whose denominator is this common denominator.Carry out the subtraction on the new numerators to give the numerator of the answer.Simplify the result for the final, simplified answer.First you find a common multiple of the denominators. The least common denominator is handy but not essential. This number will be the denominator of the answer - before simplification.For both fractions find an equivalent fraction whose denominator is this common denominator.Carry out the subtraction on the new numerators to give the numerator of the answer.Simplify the result for the final, simplified answer.First you find a common multiple of the denominators. The least common denominator is handy but not essential. This number will be the denominator of the answer - before simplification.For both fractions find an equivalent fraction whose denominator is this common denominator.Carry out the subtraction on the new numerators to give the numerator of the answer.Simplify the result for the final, simplified answer.
That's the least common denominator.
Finding the prime factorizations of the denominators will help you find the least common denominator. Converting to equivalent fractions with like denominators will allow you to subtract them successfully.