A-3.1 Explain the nature of economic costs. Distinguish between
 different types and verify that normal profit is a cost.

A-3.2 Explain the law of diminishing returns. Show it graphically.

A-3.3  Draw and explain short run total, average and marginal costs.
 Support your explanation with the law of diminishing returns.

A-3.4 Draw average and marginal cost curves, and study their
 intersection.

A-3.5  Give reasons for the existence of economies and diseconomies
 of scale.