There are twelve wires that run from your cellar to your roof. Unfortunately on their journey they could be randomly mixed up, so you can't tell which cellar wire-end corresponds to which roof wire-end. You have a battery and a light bulb, and you can temporarily twist wires together. You can also travel from the cellar to the roof and back again any number of times. Thus you can construct circuits and test the wires at either end in order to deduce what is going on. But it’s a long way to the roof. So, starting at the bottom, what is the minimum number of journeys you have to make, in order to work out exactly which wire-end in the cellar corresponds with which wire-end on the roof?

answer is the absolute best that could be found is the combination of six pair in one trip using the light bulb and battery.
first tie/twist two wires together in a pair, do the same for the other 10 wires... six pairs of wire.
go to the roof touch one end of the battery to the bulb touch one wire to the other teminal of the bulb now touch each other indiual wire to the unused end of the battery... when the bulb lights its a comlete circut. do the same for the rest of the wires.
why six pairs? a battery will light a bulb in either direction of current flow.

Posted by tom on 2004-07-14 13:39:40