Money Bags

[mmiguel]

Three bags are marked $10, $15, and $20. One bag contains two $5 dollar bills, one contains a $5 and a $10 bill, and one contains two $10 bills. You are told that no bag contains the amount of money that is marked on its exterior. You are allowed to select a bag and extract a bill. How many times must you do this before before you can guarantee that you know the contents of all three bags? What is your strategy?

[phil1882]

take a bill from the one marked 15. if you get a 5 you know it is the double 5 bag.

further more, you can deduce that the 20 bag must have 15$ and the 5 bag must have 20$

similarly with drawing a 10 out of the 15 bag.