perplexus.info :: Weights and Scales : Take the right one

Take the right one (Posted on 2013-10-18)

Among 100 coins exactly 4 are fake. All genuine coins weigh the same; all fake coins, too. A fake coin is lighter than a genuine coin.

How would we find at least one genuine coin using two weighings on a balance scale?

Source: 2010 Euler math Olympiad in Russia- authored by A.Shapovalov

No Solution Yet Submitted by Ady TZIDON

Rating: 3.0000 (1 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)

question for Kenny

| Comment 2 of 18 |

"The trickier part is what to do when the original four coins DO balance the scale. The possibilities are:
FF vs. FF
RR. vs. RR"

You don't consider the possibility RF vs RF. Your next step gives RRFF on one side of the scale and potentially the same on the other, which is a dead end.

Posted by xdog on 2013-10-18 21:27:49

Please log in:

Login:
Password:
Remember me:

Sign up! \| Forgot password

Search:

Search body:

Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (24)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:


perplexus dot info