Warning: Do not read other posters' comment unless you give up since it usually contains the answer. Clutchcity.net posters are very smart. Another relatively simple one: A foreign mathematician is captured by Sadam Hussein and were to be executed. Luckily, Sadam was in a good mood and he gave a chance to the guy to save his life if he could answer this riddle. The guy was given nine coins. One of the nine coins is counterfeit. The counterfeit coin looks very much alike the others and can only be distinguished by weight - it's lighter than the others. The mathematician is given a chance to use a balance scale "only twice" to find the counterfeit coin. How will he do it? Note: This has been answered by Invisible Fan Previous Logic riddles Riddle #1: Water Container http://bbs.clutchcity.net/php3/showthread.php?s=&threadid=52045 Answered by: drapg, SmeggySmeg Riddle #2: The Wizard and 3 Caps http://bbs.clutchcity.net/php3/showthread.php?s=&threadid=52048 Answered by: codell Riddle #3: The Wizard and 3 Caps (Advanced) http://bbs.clutchcity.net/php3/showthread.php?s=&threadid=52050 Answered by: codell Riddle #4: Average Speed http://bbs.clutchcity.net/php3/showthread.php?s=&threadid=52112 Answered by: Major, codell
Answer: Divide the coins into three even groups. Weigh group 1 against group 2. If evenly balanced, then divide group 3 into three seperate coins. If ones lighter than the other among group 1 and group 2 then divide the lighter group into three seperate coins (knowing that the counterfeit coin is in that group) Among the three newly seperated coins, weigh one against the other. The lighter one is the counterfeit. If balanced, then the one not weighed is the counterfeit.
Invisible Fan got it, although his explanation wording may be confusing to some But I got what you mean and you're correct.
