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Price elasticity of demand measures the responsiveness of changes in quantity demanded to a change in price of the product. It is measured by the formula:
For example, if the price of butter is reduced by 10% and the demand increases by 20%, the price elasticity of demand is +2.
Goods with a price elasticity of less than 1 are said to be inelastic. Goods with a price elasticity greater than 1 are said to be elastic. Necessities such as water tend to be inelastic: the demand remains much the same even if the price changes considerably.
Income elasticity of demand measures the responsiveness of changes in quantity demanded to a change in income. It is measured by the formula:
For example, if incomes rise by 10% and the demand for meat increases by 20%, then the income elasticity of demand is +2.