Twenty metal blocks are of the same size and external appearance; some are aluminum, and the rest are duraluminum, which is heavier.

Using a pan balance to determine how many blocks are aluminum, what is the minimum number of weighings to be done?

(In reply to Thoughts, spoiler? by Erik O.)

"If after 10 weighings each pair ended up in the queue to be weighed further, choose one block from the first pair as the 'standard' and weigh one from each remaining pair to determine if that pair is heaver/lighter or the same as the standard.  This would take a total of 14 weighings."

I don't understand why this is 14 weighings and not 19.

Posted by ajosin on 2005-06-03 02:32:08