I solved this two ways -- which do you prefer??
19:30
the Stolarsky mean
23:39
from an integral to a differential equation
20:19
Amadores acabaram de resolver um problema de matemática de 30 anos
14:03
two ways, one sum
15:24
Romanian Mathematics Olympiad
6:37
Believe in geometry, not squaring both sides!
27:40
The Biggest Misconception in Physics
18:36