perplexus.info :: Weights and Scales : A Bag of Fake Coins

A Bag of Fake Coins (Posted on 2003-07-25)

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?

Submitted by Brian Smith

Rating: 4.2143 (14 votes)

Solution: (Hide)

It is possible to have 169 bags and still be able to determine the bag containing the fake coins. Brian Wainscott's comment found here outlines the process.

Comments: ( You must be logged in to post comments.)

Subject	Author	Date
re: 182	David Frazer	2004-01-22 18:12:37
re: 182	Brian Wainscott	2004-01-15 14:04:26
182	Dan Porter	2004-01-15 11:35:15
possible solution?	Angel	2003-08-25 01:56:26
My best so far	Brian Wainscott	2003-07-29 09:12:23
re(6): solution (plus one)--Still more	Brian Wainscott	2003-07-29 06:42:48
re(5): solution (plus one)--Even More	Charlie	2003-07-28 15:53:01
re(4): solution (plus one)--Even More	Charlie	2003-07-28 15:50:13
No Subject	Charlie	2003-07-28 15:49:36
re(3): solution (plus one)	Brian Wainscott	2003-07-28 13:35:23
re(2): solution (plus one)	Charlie	2003-07-26 10:18:22
re: solution (plus one)	Bryan	2003-07-25 12:55:31
re: the math... the wrong math	Rich Rocket	2003-07-25 11:14:48
the math	Rich Rocket	2003-07-25 11:11:47
solution	Charlie	2003-07-25 11:08:52
A start	Lewis	2003-07-25 09:49:02

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