### Author Topic: A Riddle  (Read 10687 times)

#### Sebastian_Mares

• Guest
##### A Riddle
« on: 27 Feb '06 - 21:16 »
You are alone in a house with three floors. In the third floor, there is a light bulb. In the basement, there are three switches. One switch turns the lamp in the third floor on and off while the other two switches have no function. You cannot see the third floor from the basement, nor can you see which of the three switches has a function. Your job is to find out which switch is responsible for the light bulb in the third floor. You are allowed to go upstairs only one time.

How do you find out which switch turns the light bulb on and off?

#### Torkell

• Posts: 1169
##### Re: A Riddle
« Reply #1 on: 28 Feb '06 - 15:32 »
Turn on one switch. Wait a while (10min or so), then turn that switch off and turn another on, then quickly head to the third floor. If the light is on, then the second switch does it. If the light is off, then check if the bulb is warm. If so, the first switch controls it, otherwise, the third switch controls it.

Of course, this'll be harder to do with modern energy-saving bulbs.

#### raina

• Posts: 1163
##### Re: A Riddle
« Reply #2 on: 28 Feb '06 - 17:05 »
Consider all the dimensions.. I hate these things for making me feel so stupid. Well, maybe it's just the truth and I should accept it already.
« Last Edit: 28 Feb '06 - 17:06 by raina »

#### Sebastian_Mares

• Guest
##### Re: A Riddle
« Reply #3 on: 1 Mar '06 - 13:40 »
Turn on one switch. Wait a while (10min or so), then turn that switch off and turn another on, then quickly head to the third floor. If the light is on, then the second switch does it. If the light is off, then check if the bulb is warm. If so, the first switch controls it, otherwise, the third switch controls it.

Of course, this'll be harder to do with modern energy-saving bulbs.

Bingo!

Maybe I should have stated that the light bulb is initially off.

#### Ian @ un4seen

• Posts: 21024
##### Re: A Riddle
« Reply #4 on: 1 Mar '06 - 15:05 »
Clever. I'd have said take the faceplate off the switches - as 2 have no function, they'll probably have no wires connected. Wouldn't have to go back up stairs to check either

#### Rah'Dick

• XMPlay Support
• Posts: 946
##### Re: A Riddle
« Reply #5 on: 14 Mar '06 - 19:22 »
I'd have suggested to wait until nightfall, then flip the switches and look outside the basement window and watch, whether any of the switches did something.

#### raina

• Posts: 1163
##### Re: A Riddle
« Reply #6 on: 14 Mar '06 - 19:37 »
What a team we bunch make: the astute one, the straight approach one, the meditative and finally, the stupid one (that would be me).

#### Wraith

• Posts: 190
##### Re: A Riddle
« Reply #7 on: 15 Mar '06 - 16:21 »
Hmm... I think the answer for 'how many programmers will it take to replace a burned out light bulb?' fits here too... For a programmer, of course.
How would you call this approach?