1) Economics is the study of how societies satisfy unlimited wants and needs with limited resources. It examines the choices we must make due to scarcity.
2) Resources are limited but needs and wants are unlimited. This creates scarcity, where we cannot have everything we want. We must choose where to allocate resources.
3) Opportunity cost is the next best alternative given up when making a choice. It measures the value of the forgone alternative. Scarcity forces us to consider opportunity costs when making economic decisions.