To find the GCF:
-- List the factors of the first number.
-- List the factors of the second number.
-- Make a short list of the factors that show up for BOTH numbers.
-- Find the biggest number on the short list.
Factors of the first number (99): 1, 3, 9, 11, 33, 99 .
Factors of the second number (121): 1, 11, 121 .
Short list (factors that show up for both numbers): 1, 11
Biggest number on the short list: 11
