A geography teacher lists 12 South American countries on the chalkboard. She asks each student in her class to write a report comparing 3 of the countries. How many ways are there to select 3 of the 12 countries

There 220 ways to select 3 of the 12 South American countries for the Geography assignment that solved by using the theory of combination in mathematics. The combination in mathematics is a way of choosing items from a set of items. The combination formula is n x (n-1) x ... x (n - k + 1) / k x (k-1) x ... x 1 where n is the number items in the set which is 12 and k is the amount you want to combine from the set which is 3.