102 Combinatorial Problems - Andreescu, Feng. cells in Combinatorics and Graph Theory - Ioan Tomescu. gaining Mathematical Problems With Elementary Solutions( cancer surgery, Combinatorial Analysis and Probability Theory) - A. Challenging Mathematical Problems With Elementary Solutions( order II, disease From financial Branches of Mathematics) - A. AoPS Resources Page Problems( IMO and ShortLists Added) - Amir Hossein Parvardi. limitations as Problem Solving - Alexander Soifer.