Sent to you by Pat via Google Reader:
Here is a favorite puzzle that I learned from my father many years ago:
The puzzle does not involve any tricks. The bottles are opaque etc. Note you can assume that you know what the correct weight is, say 10 oz. I will post an answer in the extension to this post tomorrow for those of you who want to sleep on this. You can also find the answer in the comments but no peeking.
There are 10 machines that fill bottles of soda. One of the machines is either putting one ounce (of mass) too much or one ounce too little in the bottles that it produces. You have a digital scale. In one weighing figure out which of the 10 machines is off.