Question

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

Answer 1

Newton's symbol


`C_(12)^3={12\choose 3}=(12!)/((12-3)!*3!)=(12!)/(9!*3!)=(9!*11*\\ot12^2)/(9!*\\ot3*\\ot2*1)=11*2=22`

Answer = 22