a. Graphically represent and explain why the shape of the demand curve is different for firms in a perfectly competitive, monopolistic competitive and monopoly market structure.

b. Assume labour is the only variable input, use a numerical example and explain the relationship between marginal product of labour, marginal returns and marginal cost.

c. Use graph (s), illustrate and explain the relationship between marginal cost and average total cost.

d. Which stage of the relationship between marginal cost and average total cost will profit start to decline.Explain.