2006 Combinatorics #1: Vernonia High School
Source:
July 31, 2012
Problem Statement
Vernonia High School has 85 seniors, each of whom plays on at least one of the school’s three varsity sports teams: football, baseball, and lacrosse. It so happens that are on the football team; are on the baseball team; are on both the football and lacrosse teams; are on both the baseball and football teams; and are on both the baseball and lacrosse teams. Compute the number of seniors playing all three sports, given that twice this number are members of the lacrosse team.