Prime numbers are defined as numbers which only have two different factors, they are 1 and those numbers themeselves. For example 2 which only has factors 1 and 2. Another example is 3 which only has two different factors, namely  1 and 3
Prime factorisation is a process to find the prime factor of a number. One of the methods used is using a factor tree
Find the prime factors and prime factorisation of 18 



Thereby, prime factors of 18 are 2 and 3, while prime factorisation of 18 is 2 x 3 x 3
HCF is the highest common factor of a number, while LCM is the lowest common multiple of a number. To find HCF and LCM by prime factors, you should have understood how to find prime factors of a number.
Find the HCF of 30 and 3


The prime factors of  30 and 36 using the following factor trees
Prime factorisation of 30 = 2 x 3 x 5
Prime factorisation of 36 = 2 x 2 x 3 x 3 = 22 x 32
The product of the same prime factor by the smallest power is 2 x 3 = 6
So, HCF of 30 and 36 is 2 x 3 = 6 

Find the LCM of 30 and 3

The prime factors of  30 and 36 using the following factor trees
Prime factorisation of 30 = 2 x 3 x 5
Prime factorisation of 36 = 2 x 2 x 3 x 3 = 22 x 32
The product of all prime factors and the greatest power is 22 x 32 x 5 = 180
So, LCM of 30 and 36 is 180


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