This week's "Car Talk" puzzler (involves counterfeit coins)

RAY: This puzzler came to us from Clive Woods. 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?”​

http://www.cartalk.com/content/counterfeit-quarters?question

 

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Gosh, that's tedious and boring! Besides that, my attention span is..... what were we talking about again?

 

Being an organized chap, he placed the stack of counterfeit coins on a slip of paper with a "C" on it.

Chris

 

I know! I know!

Of course I'm not going to post it here. I want to win that Car Talk Plaza parking permit myself!

 

That's easy. Take one coin from each stack and put it on the scale. Take away one coin at a time and note the new weight and thus the weight of the coin. Eventually, you'll find out which was off by a gram. Now, what did I win?

 

Same as seattle, expect in the opposite direction.

Put on one coin, then add one at a time, stop when the weight is wrong, that is the bogus pile

 

I don't think that counts as "one weighing".

 

Dang. I thought by "in one weighing" they meant weighing each stack one time.

Edit: what @-jeffB said

 

Take one coin from pile 1, 2 coins from pile 2, 3 from pile 3, etc. Weigh the bunch of them. If they were all good, they would weigh 55*good grams. The amount they're off of that (in either direction) will tell you which pile had the bogus coins.

 

take 1 coin from pile 1, 2 coin from pile 2, etc.

place them on the scale and do the math.

 

why not just call him on the phone an ask him which pile is bogus?

 

Get an intern to do it?

 

Aw, man, now everybody will send in the right answer.

But I'll bet nobody else mentioned weight loss due to coin wear.

 

Too late. The shows you're hearing today are reruns. Since Tom Magliozzi died, there have been no new radio shows.

 

I think this is actually the best answer!

 

I was confused. If you go to the page where you can submit an answer online, they mention a nominal prize (the "parking pass"), different from the "Shameless Commerce Division" gift certificate they always mentioned on the air.

I saw that this question only mentioned Ray, so I thought maybe they were still posting new puzzlers. But I just looked at last week's, and it includes a recorded segment with the answer, featuring both brothers. So I guess the puzzlers are reruns, too.

This is one advantage of not having total recall -- even the stuff you've heard before can seem new!

 

Those shows and the website are still fun even though I've seen and heard it all before.

 

.....lmao