The full form of LCM is * lowest common multiple*. Means the smallest number which is multiple of all the given numbers.

for example :

LCM of 3 & 5 is 15 means 15 is the smallest number which is multiple of both 3 and 5.

LCM of 2,3 and 5 is 30 means 30 is the smallest number which is multiple of 2,3 and 5.

You can find LCM of given numbers by prime factorization method.

Facts :

1. LCM of 2 consecutive numbers is always their product. e.g. LCM of 4 and 5 will be 4 x 5 = 20

2. LCM of 2 prime numbers is always their product. e.g. LCM of 5 and 7 will be 5 x 7 = 35.

3. HCF x LCM = product of both the numbers ( for 2 numbers only)