Alina and Joe are both thinking of the same positive number. Alina tells Joe that her number is a factor of 9, while he tells her that it is a factor of 12. If the number is not 1, what is it?
I need to find a positive number that is a common factor of 9 and 12, other than 1. One way to do this is to list all the factors of 9 and 12, and see which ones they have in common. The factors of 9 are 1, 3, and 9. The factors of 12 are 1, 2, 3, 4, 6, and 12. The common factors are 1 and 3. Since the number is not 1, it must be 3. 