1960s
A peasant sells a bag of potatoes for $10. His costs amount to 4/5 of his selling price. What is the profit?

1970s
A farmer sells a bag of potatoes for $10. His costs amount to 4/5 of his selling price i.e. $8. What is the profit?

1970s (new math)
A farmer exchanges a set P of potatoes with M of money. The cardinality of the set M is equal to $10 and each element ofM is worth $1. Draw 10 big dots representing the elements ofM. The setC of production costs is composed of 2 big dots less than the setM. RepresentC as a subset ofM and give the answer to the question: What is the cardinality of the set of profits?

1980s
A farmer sells a bag of potatoes for $10. His production costs are $8 and his profit is $2. Underline "potatoes" and discuss with your classmates.

1990s
A farmer sells a bag of potatoes for $10. His production costs are 0.80 of his revenue. On your calculator graph revenue versus costs. Run the "POTATO" program to determine the profit. Discuss the result with students in your group. Write a brief essay that analyzes this example in the real world of economics.