Assuming the price elasticity of demand for textbooks is 2, and the price of the textbook gets increased by 10%, by how much does the quantity demand fall?

Answer: 20%.

Mathematically, the price elasticity of supply is simply the (%change in quantity supplied ) / (% change in price). In this case, price elasticity of supply is . This means for each 1% change in price, quantity supplied changes by 2%. So when price increased by 10%, quantity supplied will fall by 2*10=20%.

For future refrence, when elasticity of supply is less than 1 we call it inelastic, when it is above 1 we call it elastic.