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Factors-a number can be evenly divided without a remainder
Examples: Factors of 16 are 2, 4, 8. Factors of 24 are 2, 3, 4, 6, 8, 12.
Multiples-result of multiplying by a whole number.
Examples: Multiples of 2 are 2, 4, 6, 8, 10, etc. See how you are just counting by 2's? Multiples of 6 are 6, 12, 18, 24, 30, etc.
Common are obviously the ones that each number has in common. List both, like I did above, and see which numbers are in both groups. Post specific questions with your answer if you'd like them checked.