(A note from Maury Maille: due to the holidays, we opted to slack off even more than normal here at Car Talk Plaza, and we featured an encore presentation. As a result, you have a bonus week to attempt to solve the current puzzler. You're welcomeÑand good luck!)

RAY: This puzzler came to us from named Clive Woods. Thanks, Clive. I think.

Clive writes, "I work in the Anti-Counterfeit Department of the U.S. Treasury. The other day, my assistant was sent 100 U.S. quarters, and he found that 10 of them were booooogus.

"He sorted the 10 bogus coins into one pile, and being an organized sort of chap, he made 9 piles, each containing 10 of the real coins. The weight of the counterfeit coins in this case was different from the weight of a real quarter by 1 gram. However, he forgot whether it was 1 gram more or 1 gram less, but, he knew that the bogus coins were all 1 gram heavier or 1 gram lighter than the real coins."

"He was called away to another job, and he left the 10 piles on his desk. I had to determine which was the bogus pile. To do it, I had a calibrated scale that would tell me the weight placed on it within a fraction of a gram.

"The question is, how could I figure which was the pile of bogus coins in one weighing?"

Got a clue what tricks they're using at the Anti-Counterfeit Department?

Think you know? Drop Ray a note!

And tell him your answer.

[ Car Talk Puzzler ]