To encourage public transportation, Russom wants to give some friends envelopes with bus tickets and subway tickets in them. If he has 18 bus tickets and 12 subway tickets to split equally among the envelopes, and wants no tickets left over, what is the greatest number of envelopes Russom can make?

To answer the question, you will want to find the biggest way to divide both 18 and 12.

This is called the greatest common factor.

You can list all the factors (ways to divide) of each number and find the biggest one.

12 - 1, 2, 3, 4, 6, 12

18 - 1, 2, 3, 6, 9, 18

The greatest they share is 6.

Russom can make 6 envelopes.