Read the sections on Demand, Supply, Market Equilibrium, and Government Intervention and Disequilibrium for a mathematical exposition of the demand and supply model, clicking through to the next when you have finished each page. The chapter also covers price ceilings and price floor analysis as well as quantity regulations.

**Proportional Tax:**Otherwise known as a flat tax, a flat tax rate is applied to all earned income regardless of how much the taxpayer earns. So a person making $20,000 would pay the same rate as a person making $120,000, but would pay significantly less in real dollars.**Progressive Tax:**The more a person earns, the higher the tax rate. Generally in a progressive tax system, income is divided into "brackets". For example, assume a tax system divides earners into people two groups. Those who earn less than $100,000 pay 10% and people who earn $100,000 or more pay 20%. A person earning $20,000 would have to pay 10%, or $2,000, while a person who earns $120,000 would have to pay 20%, or $24,000.**Regressive Tax:**In a regressive tax system, poorer families pay a higher tax rate. Although a regressive tax system is never explicitly used, some claim a sales tax is a type of regressive tax. Since high income earners spend a lower proportion of their income on goods and services in comparison to low income earners, the rich tend to pay proportionally less sales tax.