Last week I purchased a burger and fries at McDonalds for $3.58. The
counter girl took my $4.00 and I pulled 8 cents from my pocket and
gave it to her. She stood there, holding the nickel and 3 pennies. While
looking at the screen on her register, I sensed her discomfort and tried to
tell her to just give me two quarters, but she hailed the manager for
help. While he tried to explain the transaction to her, she stood there
and cried. Why do I tell you this?

Because of the evolution in teaching math since the 1950s:

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 sells a truckload of lumber for $100. His cost of
production is $80. Did he make a profit?

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
A logger cuts down a beautiful forest because he is selfish and inconsiderate and cares
nothing for the habitat of animals or the preservation of our woodlands. He
does this so he can make a profit of $20. What do you think of this way
of making a living?

Topic for class participation after answering the question: How did
the birds and squirrels feel as the logger cut down their homes? (There
are no wrong answers.)

Teaching Math In 2005
Un ranchero vende una carretera de madera para $100. El cuesto de
la produccion era $80. Cuantos tortillas se puede comprar.