Art of Problem Solving Beast Academy 2C Guide and Practice $30 : Measurement : The measurement chapter focuses on length and includes using a ruler, estimation, customary and metric units, conversions, mixed measures, and adding and subtracting measurements. Strategies (+&−) : Rearranging addition and subtraction, canceling, subtracting everything at once, using parentheses, and skip-counting. Odds & Evens : Odds and evens, doubling, halving, addition and subtraction patterns, working with more than two numbers, and puzzles involving crossings, coins, checkerboards, and graphs.