  There are many papers written on the Two Envelopes Problem that usually study
some of its variations. In this paper we will study and compare the most
significant variations of the problem. We will see the correct decisions for
each player and we will show the mathematics that supports them. We will point
out some common mistakes in these calculations and we will explain why they are
incorrect. Whenever an amount of money is revealed to the players in some
variation, we will make our calculations based on the revealed amount,
something that is not achieved in other papers.
