In a pile, there are 11 coins: 10 coins of common weight and one coin of different weight (lighter or heavier). They all look similar.

Using only a balance beam for only three times, show how you can determine the 'odd' coin.

Open problem (i cannot solve this myself): how many more coins (with the same weight as the ten) can we add to that pile so that three weighing still suffices? My conjecture is zero, though my friend guessed that adding one is possible. The best bound we can agree upon is < 2.

i know this is not supposed to be a mathematician's forum but cant help it ;)

"find g(n), or upper/lower bounds of g(n), the maximal number of coins from which we can determine the odd coin by n weighings. e.g. g(2)=9, g(3)=12."

Posted by theBal on 2002-05-02 10:00:06