Demand curve facing a firm in a perfectly competitive market--each firm is so small and there are so many firms that none can affect price--they are...

Demand curve facing a firm in a perfectly competitive market--each firm is so small and there are so many firms that none can affect price--they are price takers. For normal goods income elasticity of demand is positive (if income goes up, demand goes up) For inferior goods, if income goes up, demand goes down. Example? For normal goods income elasticity of demand is positive (if income goes up, demand goes up) For inferior goods, if income goes up, demand goes down. Example?