The original riddle was:
You are outside a room with 5 light switches. You cannot see in the room. You don’t have anyone else to help you. You enter the room. Inside the room are 5 lights. You then find out which light switch controls which light.
And here, finally, is the “correct” answer:
While outside the room, you use the switches. You turn 1 and 2 on, 3 off. Then you turn switches 4 and 5 on and off, on and off, on and off very fast for 10 minutes. Finally, you set switch 2 and 5 off and 4 on:
| Beginning | After 10 minutes… | |
|---|---|---|
| Switch 1 | On | On |
| Switch 2 | On | Off |
| Switch 3 | Off | Off |
| Switch 4 | On, off, on, off… | On |
| Switch 5 | On, off, on, off… | Off |
Then you enter the room and look for the light that is off, but hot – this is light 2. Find the light that is on – this is light 1. Remove the remaining bulbs from the sockets and jiggle them. Two of them have burned out – the other one is light 3. Put light 3 into one of the remaining sockets. If it lights up, this is light 4, if it doesn’t, this is light 5.
Nobody got this answer. However, one alternate answer was accepted (+2):
Turn on lights 1, 2, 3 and turn off light 4. In two minutes, turn off light 2. After another two minutes, turn off light 3. Enter the room to find one light on, one light warm, one light very hot and one light off.
- Su
This answer was given just when the problem was being updated, so I took it (even thought is handles 4 lights). The best part is that since this answer is so different, it can be combined with my answer above to solve the 6 lights riddle.
Duncan put up the following answer which did start with the “three light riddle”:
You have 4 switches (A,B,C,D). Turn on switches A and B for about 5 minutes. Turn off switch B, turn on light D, and enter the room.
A=(Hot, On) B=(Hot, Off) C=(Cold, Off) D=(Cold, On)
This only works if you know how the off and on positions correlate to the lights.
I’m assigning this (+1, -1) points because I don’t like the assumption that lights don’t get hot immediately when on. But I do like the assumption that up is on, down is off (especially since when you enter the room you could conceivably find no light switches, implying that these are two-way switches and not three-way switches).
Also, many people tried the cop-out answer I was expecting:
The switches are labeled.
I was prepared to give points for this if nobody produced a “real” answer. So don’t get mad at me, get mad at her.
THE SCOREBOARD SINCE 2002:
- name/wins/losses
- minamhere 3 1 *
- yolanda_june@msn 3 0 (aa)
- hardlypoetic 2 0
- kalicokiki 2 1
- tsunami0009/bluegreensteve 2 2
- trom37 2 0
- chickennuggest 2 0
- genuine669 2 0
- adaninthelife/revolver63 2 1
- adeedas476 1 0
- blackbandit79 1 0
- walt758usa 1 0
- theriault06 1 0
- sabrosa529 1 0
- pinball10 1 0
- srmascot2002 1 0
- fester2133 1 0
- serenitysir 1 1
- punkkitten429 1 0
- debjulcoh 1 1 *
- absolutmaveric 1 0
- anven 0 1
- wonderslack 0 1
- Zubie919 0 1
- flyingelmo2004 0 1
- dirteharry503 0 1
- yodude38 0 1 *
- vvanbelle.t@gmail.com 0 1 *
- nacnud1983 2 2 * (retroactively updated as per https://fulldecent.blogspot.com/2009/01/riddle-upgraded-one-about-lights.html)
- lehighace06 0 2
- llgirl714 1 3
- gosujohn 0 3
- snoop2828 1 3
-
- denotes a recent win/loss
- aa denotes an alternate answer (huge win)
Find other riddle posts on this blog.
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