Monty Hall Say you participate in some game, you have 3 envelopes, one of them has a million dollars check and the others full with nothing. You choose one envelope randomly (say envelope number 1), the host than open envelope number 3 and show you that this envelope is empty and asks you if you want to change your decision and choose envelope 2 instead. Would you change? The answer is yes! you should change your decision. Apparently choosing your decision would raise your chances to win from 33% to 66%. If you are intersted why, you can look for monty hall pardox on google.