[Tfug] [OT] A good brainteaser to flex your sad and flabby hacker brain muscles.

Joe Blais joe.blais at pti-instruments.com
Wed Apr 11 08:09:21 MST 2007


> ( Note: This is NOT a trick question--Yes, the box has power, and yes,
> the lightbulbs are screwed in, etc. There are at least two valid
> answers. )
>
>
> Bowie J. Poag, 17 minutes 5 seconds. :)
>

The solution is easier after dealing with the really difficult stuff, the
assumptions, the "etc."

Are the switches in the off position when started? can you tell if they're
off or on? can you unplug the thing?
Are the times on the box less than an hour? are they elapsed times or times
of day?  Are they similar times?
Is the 1hr exam time meaningful to the solution?  How much of the
information given means anything or is just meant to confuse?  was the thing
unplugged or plugged in before it was given to me? are the bulbs insulated
from each other?    etc...

If I could, I'd unplug the box for about 1/2 hr.  Then plug it in. Then I'd
start toggling one of the switches (50%/50%) for a few minutes (perhaps take
a clue from the times on the box).  Then after a while, flip another switch.
Then immediately open it and feel the temperature of the bulbs.  If one was
cold and on, or hot and off, it would be the one just flipped before
opening.  If one was hot and lit, or cold and off, it would be associated
with the untouched switch. If one was modrate temperature, or the other two
were hot, or the other two cold, that would be associated with the switch I
toggled.

If they were LED's I'd cuss, and say I never really wanted to work there
anyway!

Joe






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