RE: [math-fun] How we "do mathematics"

lots of math contest experience and high school teaching (...)

A (very) old one I like : Two Death Valley marathonians friends complete their run together and seek shadow in their tent nearby the finish line. The first one had prepared a fresh 5-liter tank of water in a cooling box and his friend a similar 3-liter one. They were about to start drinking when a journalist enters the tent desperately asking for water. OK, the water is divided into three equal parts -- and drunk. The thankful journalist insists to pay his share and leaves 8 dollars to be split between the two friends. How? ---- (...) and high school teaching experience, do this kind of stuff in our heads