Simple, minimalist and difficult. Two Digits is a perfect blend between insanity and happiness. You are given 9 numbers less than 100, and all you have to do is to choose two subsets with the same sum.
Estimates — owners use the Boxleiter method (reviews × 32), wishlists proxy followers × 12, revenue uses ~62% of list price × est. owners. These are rough industry heuristics, not official data.