First, write down the factors of two or three numbers in the topic (both, you can't find them without them), then find the same number and the largest one.

For example:

Excuse me: What is the greatest common factor of 24 and 36?

Answer: The factors of 24 are 1, 24,2,12,3,8,4,6.

Factors of 36: 1, 36,2,18,3,12,4,9,6.

Common factor: 1, 2,3,4,6, 12.

Maximum common factor: 12

A: The greatest common factor of 24 and 36 is 12.

Another method is short division. Let me give you an example directly.

For example:

Excuse me: What is the greatest common factor of 24 and 36?

Answer: 24=2*2*2*3.

36=2*2*3*3

Common factors: 2,2,3.

2*2*3= 12

A: The greatest common factor of 24 and 36 is 12.

I hope it helps you!