Imagine you are on a television show. The presenter asks you to choose one of two sealed envelopes. Both envelope A and envelope B contain some money, but the host does not tell you how much money is in each. The only thing he says is that an envelope contains the **twice as much money as the other**.

You choose envelope A, open the envelope and find that inside it is $ 100.00 (one hundred reais). The presenter then offers you the following offer: you can either get the $ 100 or choose to change envelopes by choosing envelope B.

This way, you can do the following reasoning: Because one envelope contains twice as much money as the other, envelope B can contain either $ 200 or $ 50, with the same probability for each. Since I have more to gain (+ R $ 100) than to lose (-R $ 50), I should make the switch.

But just as you decide to tell the presenter that you want to change envelopes, a thought arises: If you had chosen envelope B - whether you had earned $ 200 or $ 50 - you would have arrived exactly the same conclusion. Therefore, if the above argument is valid, you should change envelopes regardless of the initial choice. Does that make any sense?