(A) Fully factorise both numbers:
So 18 = 2*3*3 and 45 = 3*3*5
(B) For the gcf write down only those numbers (factors) that appear in both factorisations. If they appear twice in both factorisations, write them twice for the gcf.
So here we have gcf = 3*3
[there is no 2 in the factorisation of 45 so no 2 in the gcf. Likewise, no 5 because it is not there for 18.]
(C) Multiply the numbers in the gcf together so gcf = 9.
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The factors of 18 are:
1, 2, 3, 6, 9, 18
The factors of 45 are:
1, 3, 5, 9, 15, 45
The common factors are:
1, 3, 9
The Greatest Common Factor:
GCF = 9
The greatest common factor of 18 and 55 is 1.
The greatest common factor of 39 and 18 is definitely 3.
The Greatest Common Factor of 40 and 18 is 2.
The greatest common factor of 18 , 7 = 1
The greatest common factor of 18 and 100 is 2