Enter GCF or LCM numbers:
Determine GCF(18,21)
GCF = Largest factor that divides numbers
Determine the factors for 18
1,2,3,6,9,18
Determine the factors for 21
1,3,7
List the common factors
1,3
GCF(18,21) = 3
Evaluate GCF
Since GCF ≠ 1, they are not relatively prime (co-prime)
Since GCF ≠ 1 and have a difference of two, the numbers are not twin prime
Calculate LCM for the following
(18,21)
List the first few multiples for 18
18,36,54,72,90,108,126,144,162,180
List the first few multiples for 21
21,42,63,84,105,126,147,168,189
LCM is the smallest common number:
LCM(18,21) is 126
