Art of Problem Solving Beast Academy 2B Guide and Practice $30 : Subtraction : Place value strategies, using addition, finding a difference, counting up, subtracting then adding, subtracting all at once, and subtracting in parts. Expressions : Evaluating expressions, using parentheses, working with symbols, simplifying, and solving equations. Problem Solving : Guessing and checking, working backwards, drawing a picture, finding useful information.