Elasticity, in general, is used to quantify the response of one variable when another variable changes. 

It measures the responsiveness of demand to changes in price.

It is always negative because of the law of demand.

Goods with close substitutes tend to have more elastic demand than the goods that don’t have close substitutes. Since the food market is defined in broad sense, it does not have close substitutes compared to the hamburger market which has many close substitutes. Thus, we expect hamburger market to have more elastic demand than the food market.

Demand is inelastic when the percentage change in quantity demanded is smaller than the percentage change in price. Inelastic demand always takes a value between zero and -1.

Demand is elastic when the percentage change (decrease) in quantity demanded is larger than the percentage change (increase) in price. Elastic demand has an absolute value greater than 1.

The price elasticity of demand measures how much quantity demanded of a good changes when there is a change in the price of the good. It measures the price sensitivity or responsiveness of consumers and it is calculated as the percentage change in quantity demanded divided by the percentage change in price. Generally, it is thought that the price elasticity of demand can be understood by simply looking at the slope of a demand curve. The flatter the demand curve, the higher the price elasticity and the steeper the demand curve, the lower the price elasticity of demand. It should be noticed that the slope of a demand curve is different from its price elasticity of demand.

Total revenue is computed as the price of a good times the quantity sold.

When the demand is inelastic, an increase in price causes the total revenue to increase. With an inelastic demand curve, the reason why the total revenue increases with price increase is that the increase in price leads to a decrease in quantity demanded that is proportionally smaller. So, if the demand of a good is inelastic, the pricing strategy to increase the total revenue from the sales would be to increase the price of the good. As a result, the total revenue increases.

Whether or not a price hike causes total revenue from sales to increase is determined by the price elasticity of demand. If the demand of the good that the seller sells is elastic, an increase in the price causes the total revenue to decrease. A decrease in price, in contrast, causes the total revenue to increase. On the other side, when the demand of the good is inelastic, an increase in price causes the total revenue to increase.

It measures the responsiveness of demand to income  changes.

It measures how much the quantity demanded of one good responds to a change in the price of another good.

The price elasticity of supply is a measure of the response of quantity supplied of a good to a change in price.

The equilibrium price falls and the equilibrium quantity goes up. Since there is a fall in price, the revenue from sales for the sellers goes down since the demand for their product is inelastic. Recall that when the demand of the good is inelastic, an increase in price causes the total revenue to increase but in contrast a decrease in price causes the total revenue to decrease. Result indicate that technological improvements in the agriculture sector for the goods with inelastic demand cause the farmers’ income to decrease.

Price ceiling is a legal maximum on the price at which a good or a service can be sold.

Price floor is a legal minimum on the price at which a good or service can be sold.

Tax incidence is the study of who bears the burden of taxation. 

The workers bear the bulk of the burden of a payroll tax if the labor supply is relatively inelastic than the labor demand, and the firms bear the bulk of the burden of a payroll tax if the labor supply is relatively elastic than the labor demand. Labor demand is more elastic than the labor supply. Thus, it can be said that a tax burden goes more heavily on the side of the market that is less price elastic which is labor supply. So, labor pays more of the payroll tax than the employers.

Consumer surplus is the difference between the maximum amount a person is willing to pay for a good and the market price.

Efficiency is the property of a resource allocation of maximizing the total surplus received by the society.