"Teaching Math" joke

Teaching Math in 1950:
A logger sells a truckload of lumber for $100. His cost of production is 4/5 of the price. What is his profit?
Teaching Math in 1960:
A logger sells a truckload of lumber for $100. His cost of production is 4/5 of the price, or $80. What is his profit?
Teaching Math in 1970:
A logger exchanges a set "L" of lumber for a set "M" of money. The cardinality of set "M" is 100. Each element is worth one dollar. Make 100 dots representing the elements of the set "M." The set "C", the cost of production contains 20 fewer points than set "M." Represent the set "C" as a subset of set "M" and answer the following question: What is the cardinality of the set "P" of profits?
Teaching Math in 1980:
A logger sells a truckload of lumber for $100. His cost of production is $80 and his profit is $20. Your assignment: Underline the number 20.
Teaching Math in 1990:
By cutting down beautiful forest trees, the logger makes $20. What do you think of this way of making a living? Topic for class participation after answering the question: How did the forest birds and squirrels "feel" as the logger cut down the trees? There are no wrong answers.
Teaching Math in 2002:
A logger sells a truckload of lumber for $100. His cost of production is $120. How does Arthur Andersen determine that his profit margin is $60?
Teaching Math in 2010:
El hachero vende un camion carga por $100. La cuesta de production es.............