Art of Problem Solving Beast Academy 2D Guide and Practice $30 : Big Numbers : Thousands, millions and larger place values. Reading, writing, adding, subtracting, comparing, and estimating with big numbers. Algorithms (+ & -): Stacking addition with regrouping, adding more than two numbers at a time, stacking subtraction with breaking, and solving cryptarithms. Problem Solving : Staying organized, finding and using patterns, solving simpler problems, eliminating choices, and using manipulatives.