Find the HCF for : 30 and 42

To find the HCF (highest common factor) for two numbers, factor the two numbers and use the factors that are found in both numbers (the number of times that they are found in each number):

 

27  =  3 x 3 x 3

45  =  3 x 3 x 5         So the HCF  =  3 x 3  =  9

 

18  =  2 x 3 x 3

66  =  2 x 3 x 11       So the HCF  =  2 x 3  =  6

 

96  =  2 x 2 x 2 x 2 x 2 x 3

44  =  2 x 2 x 11       So the HCF  =  2 x 2  =  4