All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Logic > Weights and Scales
One or Two Fake Coins (Posted on 2005-09-13) Difficulty: 4 of 5
In a group of ten coins there are either one or two fake coins and the rest are real. The fakes can be distinguished from the real coins only by weight. If there are two fake coins they will be equal weights.

Find a strategy to identify the fake coin or coins which uses only a balance scale no more than five times.

No Solution Yet Submitted by Brian Smith    
Rating: 3.6667 (3 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Some Thoughts A confidence vote | Comment 1 of 4
It is likely it can be done.

If there's only one fake coin, it can be any of the ten, and it can be heavier or lighter, so we have 20 cases.

If there are two fake coins, we have 45 possible pairs, heavier or lighter, giving 90 cases.

The balance can produce three results (left heavier, right heavier, left equals right) so using it 5 times we could have 3^5=243 results.

As 243>90, we should be able to pinpoint the answer.

There remains only a leeeeeeeeeeeetle detail... how to do it! (Details left to the reader.)

  Posted by Federico Kereki on 2005-09-14 02:36:26
Please log in:
Remember me:
Sign up! | Forgot password

Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (0)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Copyright © 2002 - 2018 by Animus Pactum Consulting. All rights reserved. Privacy Information