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

Home > Logic > Weights and Scales
9 coins prob (Posted on 2016-01-18) Difficulty: 3 of 5
There are nine silver coins marked 1, 2, 3, 4, 5, 6, 7, 8, and 9.
They are supposed to weigh the number of grams that is written on them.
One of the coins is fake and is lighter than it should be.

Find the fake coin using the balance scale twice.

No Solution Yet Submitted by Ady TZIDON    
No Rating

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution Two preplanned weighings | Comment 3 of 6 |
Weighing 1: 1+2+9 vs 3+4+5 with 6,7,8 left off.
Weighing 2: 2+3+7 vs 1+5+6 with 4,8,9 left off.

Each of the nine possible pairs of locations for the light coin occurs one-to-one for each of the nine coins.  For example coin 4 is 1st=right, 2nd=off.

Then just by knowing which group the light coin was in each time, the light coin itself can be determined.

Edit: Corrected typo: "1+3+7 vs 2+5+6" to "2+3+7 vs 1+5+6"

Edited on January 19, 2016, 10:03 am
  Posted by Brian Smith on 2016-01-18 23:22:11

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 (2)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

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