How do you add or subtract fractions with uncommon denominators? - Answers

In order to add and subtract using non-common denominators, you must find a common denominator. The easiest way of finding one is to multiply the two denominators. But there may be a smaller number (least common denominator). Mutiply the numerator and denominator of the first number by the second denominator (effectively multiplying by 1). Then multiply the numerator and denominator of the second number by the original denominator of the first number. This will leave the denominators the same. Example : add 1/3 and 1/4 Multiply 1/3 by 4/4 to yield 4/12. Multiply 1/4 by 3/3 to yield 3/12. Add the numerators. 1/3 + 1/4 = 4/12 + 3/12 = 7/12