What is the Least Common Multiple of 7 and 21?
Least common multiple or lowest common denominator (lcd) can be calculated in two way; with the LCM formula calculation of greatest common factor (GCF), or multiplying the prime factors with the highest exponent factor.
Least common multiple (LCM) of 7 and 21 is 21.
LCM(7,21) = 21
Least Common Multiple of 7 and 21 with GCF Formula
The formula of LCM is LCM(a,b) = ( a × b) / GCF(a,b).
We need to calculate greatest common factor 7 and 21, than apply into the LCM equation.
GCF(7,21) = 7
LCM(7,21) = ( 7 × 21) / 7
LCM(7,21) = 147 / 7
LCM(7,21) = 21
Least Common Multiple (LCM) of 7 and 21 with Primes
Least common multiple can be found by multiplying the highest exponent prime factors of 7 and 21. First we will calculate the prime factors of 7 and 21.
Prime Factorization of 7
Prime factors of 7 are 7. Prime factorization of 7 in exponential form is:
7 = 71
Prime Factorization of 21
Prime factors of 21 are 3, 7. Prime factorization of 21 in exponential form is:
21 = 31 × 71
Now multiplying the highest exponent prime factors to calculate the LCM of 7 and 21.
LCM(7,21) = 71 × 31
LCM(7,21) = 21