How do you get the greatest common factor with the factor tree?

Answer 1

I'm a little different on this, but it works. We'll do 405 and 225. So you see the number 5 is the lowest common number. Divide 405/5 & 225/5. I do it like this:

5 l 405 225

81 45

Now what do 81 and 45 have in common? 3. So you do this:

5 l 405 225

81 45

3 27 15

The next step is the same. What do 27 and 15 have in common? 3 again. So:

5 l 405 225

81 45

3 27 15

One more time. What do 27 and 15 have in common? 3. So:

5 l 405 225

81 45

3 27 15

3 9 5

95 and 5 have no common number, so we're done. Now take the numbers on the left and multiply for the answer: 5*3*3=45.

A neat little trick for getting the least common multiple is to multiply every number on the left by the answers on bottom:

5*3*3*9*5=2025