This is how I find the GCF.
I find the prime factors.
63/3 = 21
21/3 = 7
7/7 = 1
81/3 = 27
27/3 = 9
9/3 = 3
3/3 = 1
Then I find the common prime factors:
63: 3 x 3 x 7
81: 3 x 3 x 3 x 3
Then I multiply the common prime factors:
3 x 3 = 9
The GCF for 63 and 81 (number 3) is 9.
I bet you can use this method for all the other GCFs! :)
For this one, find the prime factors like before, and if there aren't any besides one, then it's a prime number.
75/3 = 25
25/5 = 5
5/5 = 1
The prime factorization for 75 is 3 x 5 x 5
(I don't know the answer to 7, 8, 9, 10, 11, 12, 25, or 26, sorry!)
