The Least common multiple or lowest common denominator (lcd) can be calculated in two-way; with the LCM formula calculation of the greatest common factor (GCF), or multiplying the prime factors with the highest exponent factor.
The Least common multiple (LCM) of 15 and 20 is 60.
GCF(15,20) = 5
LCM(15,20) = (15 × 20) / 5
LCM(15,20) = 300 / 5
LCM(15,20) = 60
