text: how do i express the lcd within fractions?   it is the smallest (non-zero) number that is a multiple of the denominators. for instance, the lcd of {1/2, 1/4} is 4 because the least common multiple of 2 and 4 is 4. likewise the lcd of {1/2, 1/3} is 6.  by using this (or any multiple of it) as a denominator, it enables addition, subtraction or comparison of fractions:  1/2 + 1/4 = 2/4 + 1/4 = 3/4;  1/2 − 1/3 = 3/6 − 2/6 = 1/6;  1/3 < 2/5 since 5/15 < 6/15.