LCD is the least common multiple of the denominators of the fraction. The use of finding the LCD of a fraction is to simplify the adding, subtracting, dividing and multiplying the fractions. For ½, 2 is the least common denominator. For 3/16, 16 is the least common denominator. For 7/8, 8 is the least common denominator. Each of these fractions cannot be reduced to a simpler form because these are their simpler forms. If it can be reduced, the LCD would vary.