If the quantity demanded of a commodity increases from 20 units to 30 units when there is an increase in price from $4.00 to $5.00, the elasticity of demand...

The elasticity of demand measures the responsiveness of the quantity demanded of a commodity to a change in its price. In this case, when the price of the commodity increased from $4.00 to $5.00, the quantity demanded increased from 20 units to 30 units. To calculate the elasticity of demand, we use the following formula: Elasticity of demand = (percent change in quantity demanded) / (percent change in price) First, let's find the percent change in quantity demanded: (30 units - 20 units) / 20 units = 0.50 or 50% Next, let's find the percent change in price: (5.00 - 4.00) / 4.00 = 0.25 or 25% Finally, let's plug in the values into the formula: Elasticity of demand = 0.50 / 0.25 = 2.00 So, the elasticity of demand in this case is 2.00. This means that a 1% increase in price leads to a 2% decrease in the quantity demanded.