. A class elects two officers, a president and a secretary/ treasurer, from its 12 members. How many different
ways can these two offices be filled from the members of the class?
ways to arrange 12 in groups of 2:
binomial coefficient
C(12,2) = 12!/[2!*10!]
= 12*11/2 = 66
or use Pascal's triangle, third element in 13th row.