ABSTRACT
They are all what we call “problems.” That is, they tell us about undesirable situations that need to be fi xed, changed or otherwise improved, if possible.
Here’s a different set of situations:
Suppose that every hour of every day, an airplane leaves Los Angeles for New York City and at the same instant, an airplane leaves New York City for Los Angeles. Each fl ight takes 5 hours. In a single day, how many airplanes originating in New York City will pass airplanes originating in Los Angeles in the air?
