# Greatest common factor

Common factor of some numbers.
Greatest common factor (GCF). Finding GCF.

Common factor of some numbers  - a number, which is a factor of each of them. For example, numbers  36,  60,  42 have common factors  2  and  3 . Among  all common factors there is always the greatest one, in our case this is 6. This number  is called a greatest common factor (GCF).

To find a greatest common factor (GCF) of some numbers it is necessary:

1)  to express each of the numbers as a product of its prime factors , for example:

360 = 2 · 2 · 2 · 3 · 3 · 5 ,

2)  to write powers of all prime factors in the factorization as:

360 = 2 · 2 · 2 · 3 · 3 · 5 = 2 3 · 3 2 · 5 1 ,

3)  to write out all common factors in these factorizations;
4)  to take the least power of each of them, meeting in the all factorizations;
5)  to multiply these powers.

E x a m p l e . Find GCF for numbers:  168, 180 and 3024.

S o l u t i o n .  168 = 2 · 2 · 2 · 3 · 7 = 2 3 · 3 1 · 7 1 ,

180 = 2 · 2 · 3 · 3 · 5 = 2 2 · 3 2 · 5 1 ,

3024 = 2 · 2 · 2 · 2 · 3 · 3 · 3 · 7 = 2 4 · 3 3 · 7 1 .

Write out the least powers of the common factors 2 and 3  and multiply them:

GCF = 2 2 · 3 1 = 12 .