How do you find the GCF of 20 and 30?

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Answer 1 · 2017-01-11T00:19:55

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

First factor 20 down to its prime factors.

$2 \times 2 \times 5$ $2 xx 2 xx 5$

Second factor 30 down to its prime factors

$2 \times 3 \times 5$ $2 xx 3 xx 5$

The common factors are 2 and 5.

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

There are shortcuts that often work however

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

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