I notice that I did not mention the Production Possibilities Frontier (PPF) in a prominent way in the exam prep slides - it may be worth your while to review the concept in order to be able to explain the concept of opportunity cost (11 April 2013).
You can get an introduction to the PPF concept here (10 mins): http://www.youtube.com/watch?v=_7VHfuWV-Qg
This video on PPF is slightly more advanced: http://www.youtube.com/watch?v=a5rxIY46J7s
Here is the wikipedia link.
None of these discuss the determination of the optimum point between the two extremes (where the marginal value of the one equals the marginal value of the other).
Note 13 April 2013 - Here too are the Pretoria slides - an expansion of the exam prep slides used in Johannesburg - i have included some specific references to previous exam papers and dealt with strategies to deal with "unfair" papers.