What is the HCF of 72 and 27?

To work this out, you first need to break the numbers down into their prime factors. This gives:

72 = 2x2x2x3x3

27 = 3x3x3

The next step is to identify any common prime factors. In this case both numbers have two 3s as prime factors. Multiply these together and you get:

3x3 = 9

Therefore the HCF of 72 and 27 is 9.