A factor tree is just a way to display the prime factorization. Once you have that, you can find the GCF.
2 x 2 x 2 x 2 = 16
2 x 2 x 2 x 5 = 40
Select the common factors.
2 x 2 x 2 = 8, the GCF
16 8,2 4,2,2 2,2,2,2
Use a factor tree. 16 8,2 4,2,2 2,2,2,2
Use a factor tree. 9 3,3 16 8,2 4,2,2 2,2,2,2
16 8,2 4,2,2 2,2,2,2
24
16 8,2 4,2,2 2,2,2,2
by using a prime factor tree
Use a factor tree. 16 8,2 4,2,2 2,2,2,2
Use a factor tree. 9 3,3 16 8,2 4,2,2 2,2,2,2
16 8,2 4,2,2 2,2,2,2
16 8,2 4,2,2 2,2,2,2
16 8,2 4,2,2 2,2,2,2
16 8,2 4,2,2 2,2,2,2
16 8,2 4,2,2 2,2,2,2
16 2, 8 2, 2, 4 2, 2, 2, 2
164 42 2 2 2244 62 2 2 3The only common factors of 16 and 24 are 2, 2, and 2, so their greatest common factor is the product of 2 x 2 x 2, 8.
Divide 16 by 1, 2 and 4. 1,2,4,8,16