LCM means least common multiple, means if we are given two numbers then their LCM would be the least number which can be divided by both these number.
For eg: Let 3a, 3b be two numbers then their LCM would be 3ab.
Or let support we have 12 , 15 then then their LCM would be 60, because 60 is divisible by both.
HCF means highest common factor i.e. if we have two numbers then their HCF would be the highest number which divides both the numbers.
For eg: Let 3a and 3b are two numbers then their HCF would be 3.
Or let 12, 15 be two numbers then their HCF would be 3.
Some formulae related to LCM and HCF:
1) LCM = HCF × other factors.
Note: These other factors must be co- prime i.e. for eg (4, 5), (1, 3) etc.
2) Product of two numbers = HCF × LCM.
3) Product of n numbers = (HCF)^(n-1) × LCM.
4) LCM and HCF of rational numbers:
LCM (a/b, c/d, e/f) = LCM (a, c, e)/HCF (b, d, f)
HCF (a/b, c/d, e/f) = HCF (a, c, e)/LCM (b, d,f)