This document discusses the concept of elasticity and its applications. It defines key terms like price elasticity of demand, price elasticity of supply, and total revenue. It examines how total revenue is affected by elasticity and provides examples to illustrate applications, including how good harvests can hurt farmers, why OPEC struggled to keep oil prices high, and how drug interdiction may increase short-run crime but decrease it long-run. The key points are that elasticity determines how quantities respond to price changes, and it is important for understanding how policies impact markets and different groups within them.