You have N large bags of coins. All of the bags contain real 12 gram coins except for one, that one contains fake 11 gram coins.

To help you find the bag of fake coins, you have a digital scale which will give you the exact weight of any amount of coins up to 1500 grams. Any amount over 1500 grams will cause the scale to spit out a random value.

How many bags (N) can you have and still be able to tell which bag contains the fake coins if you can only use the scale three times?

(In reply to solution by Charlie)

Charlie, your solution is brilliant! I did notice, however, that the problem states that one bag is known to have fake coins in it, and your solution examines each of 50 bags. Thus, if NONE of the three weighings comes out light, then we know the fake coins are in bag 51.

Posted by Bryan on 2003-07-25 12:55:31