Example: The Two Envelope Problem
You are offered a choice between two envelopes. Each contains an unstated amount of cash and you are told that one of them contains twice as much as the other.
You pick one of them, open it and find $x. This means that the other envelope has either $x/2 or $2x.
You are now offered the choice of :
- Keeping what you have: $x
or
- Exchanging it for the other (unopened);
expected value: