How do you find the GCF of 20 and 30?

Jan 11, 2017

The preferred technique is to factor each number then multiply all common factors together to find the greatest common factor.

Explanation:

First factor 20 down to its prime factors.

$2 \times 2 \times 5$

Second factor 30 down to its prime factors

$2 \times 3 \times 5$

The common factors are 2 and 5.

The greatest common factor is $2 \times 5 = 10$

There are shortcuts that often work however

20 can be easily factored into $2 \times 10$ while
30 can be easily factored into $3 \times 10$

10 can then be easily be seen as the greatest common factor.