Question

A set M=(1,2,......100) is divided into seven subsets with no number in 2 or more subsets. Show that at least one subset either contains four numbers a,b,c, and d such that a+b = c+d or three number p,q and r such that p+q=2r

Answer 1

This sounds pretty cool. Any idea how to get started? Maybe start with a smaller set first?