Imagine a simple game. You are presented two envelopes and asked to choose one
of them. Then you are shown that the envelope you have selected contains
\( x \) monies. Then you are told that the other envelope contains either
\( 10 x \) or \( \frac{x}{10} \) monies (with equal probabilities).
Should you open the other envelope and take the monies in it? Or should you
keep your original envelope?
The video below has participated in "Summer of Math Exposition" competition
in 2021. It explains various ways to define and solve the two envelope
problem and provides a valuable lesson on expected values.