Answer: -0.5
Step-by-step explanation:
The price elasticity of demand is calculated as :
= % change in quantity demanded / % change in price.
% change in quantity demanded = (90 - 100) / 100 × 100 = -10%
% change in price = (12 - 10) / 10 × 100 = 2/10 × 100 = 20%
Price elasticity of demand = -10% / 20% = -0.5