Okay folks, its been a while since I've posted one of these of the logic type. So lets see whos clever enough!
There are three sealed envelopes. One contains two $5 bills, one contains a $10 and a $5 bill, and the third contains two $10 bills. Unfortunately, all three envelopes have the wrong amount marked on the outside. How could you correct all three by opening one envelope and looking only at one bill?