This is an old one. You have 12 pennies. One is fake, either lighter or heavier than the others. You also have a balance scale. How can you determine which is the bad one in 3 weighings?
Subscribe to:
Post Comments (Atom)
skip to main |
skip to sidebar
Humans—smart enough to have ideas; foolish enough to believe them
Blog Archive
-
▼
2005
(436)
-
▼
July
(43)
- Nanoparticles bearing genes
- $1.5 Billion Giveaway to Halliburton and Sugar Lan...
- 12 pennies
- Impact of estate tax repeal on the Bush cabinet
- 12 pennies
- When is 100 < 99?
- Meat-Eating Caterpillar:
- Message-Oriented-Middleware as a web service
- Greenspan Rejects Estate Tax Repeal Without Offset...
- "No nudity. No violence. Unspeakable obscenity."
- The paradox of North Korea
- It's about Bush
- Stock market technical analysis
- More peaceful spokespersons
- Showers cause brain damage
- "Cardinal says Catholics can believe that God guid...
- Who speaks for peaceful Islam?
- 256MB Flash Drive for $31,95 — with key ring link
- Useless Piles of Cash
- Catholic belief
- Yet another power curve
- JavaOne 2005
- The Wally Reflector
- The impulse for meaning
- The Terasem Movement, Inc.
- Vegetarian beef?
- Finding meaning in evolution?
- Are unions making a comeback in public opinion?
- African poverty
- Unintended consequences department: evolving small...
- Is it Rove?
- Stop the NRA
- Reform the Patriot Act
- Risk privatization
- Criminal ethics
- Tell FirstGroup to Cease US Union-Busting
- Food Freedom?
- Podcasts
- Another way Bush and his conservative cronies are ...
- How Bush is tarnishing history
- Another place to sign up to defend the court
- Supreme court nominee
- Pollack and Krugman on Iraq
-
▼
July
(43)
5 comments:
weigh 1, 2, 3, 10 vs. 4, 5, 6, 11
1, 2, 3, 11 vs. 7, 8, 9, 10
1, 4, 7, 10 vs. 2, 5, 8, 12
Once you you've done those weighings, how do you decide which is the bad coin?
each coin is in a unique group of weighings.
1 is in left, left, left
2 is in left, left, right
3 is in left, left, none
4 is in left, right, none
etc.
Also no opposite pattern to any of these is taken.
So if the scales tipped left, left, left you'd know 1 was heavier.
If it was the opposite, right, right, right, then 1 was lighter.
whoops, 4 is left, none, right.
Thanks. I guess Google knows everrything. Here are two sites that discuss this problem in detail. http://www.iwriteiam.nl/Ha12coins.html gives the answer above along with some others. http://www.cut-the-knot.com/blue/weight1.shtml gives other solutions.
Post a Comment