The Light Bulb Problem
Ok, you've all heard a gazillion of light bulb jokes. This is not
really a joke, but a problem to excercise your brain cells. I heard
this from my former boss, and I think this problem is thoroughly
enjoyable. So, here you are!
The setup
You're at the basement of a house. You have three switches, labeled A,
B and C, each of which control a single light bulb upstairs, labeled
1, 2 and 3. You cannot see the light bulbs. You know when each switch
is on (the light is lit) and when not. You do not know which switch
controls which light bulb.
The task
You must find out which switch controls which light bulb. You may
only go upstairs once. That is, you can set the switches, change them
as you like, and then go to examine the bulbs. Then you must tell which
switch controls which bulb. How can you do it?
This problem is probably easier this way, written out, than what it
is when told in person. A colleague of mine solved it at the coffee
table before I found it out, and it irritates me enormously.
Think it over!
Then check the answer here.
Published in Njet Problem! collection 1996-01-22.
