Let $A = \{1,2,3,\ldots,99\}$.
Let $S$ be a subset of $A$ with $10$ elements.
Show that there exist two disjoint subsets of $S$ such that sum of their elements is the same.
Example:
$S = \{1,4,7,9,67,70,83,85,90,97\}$ and we can choose $\{7,90\}$ and $\{97\}$ as two subsets of $S$ with sum of elements the same.