perplexus.info :: Logic : Light bulb

Light bulb (Posted on 2002-05-16)

A light bulb is hanging in a room. Outside of the room there are three switches, of which only one is connected to the lamp. In the starting situation, all switches are off and the bulb is not lit.

You are allowed to enter the room only once (the bulb is not visible from outside). How can you determine which of the three switches turns on the light bulb?

Submitted by Half-Mad

Rating: 3.2500 (24 votes)

Solution: (Hide)

To find the correct switch (1, 2, or 3), turn switch 1 on and leave it like that for a few minutes. After that you turn switch 1 back off, and turn switch 2 to on. Now enter the room. If the light bulb is lit, then you know that switch 2 is connected to it. If the bulb is not lit, then it has to be switch 1 or 3. Now touching the light bulb, will give you the answer: if the bulb is still hot, then switch 1 was the correct one; if the bulb is cold, then it has to be switch 3.

Comments: ( You must be logged in to post comments.)

Subject	Author	Date
Puzzle Solution	K Sengupta	2022-01-09 07:02:53
what about an assistant?	Pedro Felipe	2007-11-23 01:28:38
amazing !!!	assaf	2007-01-13 11:09:18
4 switches?	Andre	2005-09-02 18:00:52
Solution... Kind of...	Stephen Ticsay	2005-04-15 01:37:27
I got it!	Lisa	2004-04-21 09:36:13
re: A Funny Soultion	logischer Verstand	2004-04-13 17:21:13
my way	logischer Verstand	2004-04-13 17:18:23
An interesting way	Allison Smetana	2003-04-28 11:08:08
solution	nas	2003-01-14 07:31:37
HEY,MEL!YOU LOOKED AT THE SOULTION TO THE PROBLEM YOU CHEATER!	Megan	2002-09-07 14:47:41
A Funny Soultion	Megan	2002-09-07 10:27:30
i know the answer! hehehe i smart	Mel	2002-08-22 11:44:08
only 1 bulb	Sean	2002-05-26 07:29:50
duh!!	theBal	2002-05-17 09:49:19
Solution	page410	2002-05-17 07:32:13
easy	theBal	2002-05-16 07:33:30

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