Brainteaser.

[TheOriginalHappyGoat]

Here's an interesting puzzle form today's Guardian. See if you can figure it out (don't give it away if you already know the answer).

There are three switches in the basement. One of them controls a single lightbulb in the attic. You are tasked with taking one trip to the basement, where you can flip the switches on and off as much as you like, and then taking one trip to the attic. After this one and only trip the attic, you have to figure out which switch controls the lightbulb. How do you do it?

To clarify, you cannot see the lightbulb from the basement.

 

[NPT]

Here's what I would do....don't know if it's correct...probably not. I'm gonna label them as switch A,B, and C.

Spoiler

I would turn on two(A & B) of the switches and leave them on for 15-20 minutes then I would turn switch B off and go to the attic. If the bulb it burning it's switch A, if the bulb is hot it's switch B, and it the bulb is cold it's switch C.

 

[DougS]

Here's an interesting puzzle form today's Guardian. See if you can figure it out (don't give it away if you already know the answer).

There are three switches in the basement. One of them controls a single lightbulb in the attic. You are tasked with taking one trip to the basement, where you can flip the switches on and off as much as you like, and then taking one trip to the attic. After this one and only trip the attic, you have to figure out which switch controls the lightbulb. How do you do it?

To clarify, you cannot see the lightbulb from the basement.

Are we allowed to make any assumptions regarding the position of the switches viz a viz their on/off function. I want to assume that a switch in a down position is off, and not worry that the switch might be upside down.

 

[TheOriginalHappyGoat]

Are we allowed to make any assumptions regarding the position of the switches viz a viz their on/off function. I want to assume that a switch in a down position is off, and not worry that the switch might be upside down.

There's no trickery. On or off, however you want to picture it.

 

[TheOriginalHappyGoat]

Here's what I would do....don't know if it's correct...probably not. I'm gonna label them as switch A,B, and C.

Spoiler

I would turn on two(A & B) of the switches and leave them on for 15-20 minutes then I would turn switch B off and go to the attic. If the bulb it burning it's switch A, if the bulb is hot it's switch B, and it the bulb is cold it's switch C.

You got it. I added a spoiler to your post since you answered it so quickly. Well done.

 

[Noodle]

Here's what I would do....don't know if it's correct...probably not. I'm gonna label them as switch A,B, and C.

Spoiler

I would turn on two(A & B) of the switches and leave them on for 15-20 minutes then I would turn switch B off and go to the attic. If the bulb it burning it's switch A, if the bulb is hot it's switch B, and it the bulb is cold it's switch C.

I came up with a slight different way, but same principal. I thought it was pretty easy, as it took me all of about 30 seconds.

My way:

Spoiler

Turn on #1 and wait about 15 minutes, then turn on #2 and high-tail it to the attic. If light is not on, it's #3. If light is on and really hot it's #1. If light is on but only warm, it's #2. The beauty of my solution is that there is a 67% chance that the light will be on when I get to the attic--which might be important.

 

[NPT]

Here's an interesting puzzle form today's Guardian. See if you can figure it out (don't give it away if you already know the answer).

There are three switches in the basement. One of them controls a single lightbulb in the attic. You are tasked with taking one trip to the basement, where you can flip the switches on and off as much as you like, and then taking one trip to the attic. After this one and only trip the attic, you have to figure out which switch controls the lightbulb. How do you do it?

To clarify, you cannot see the lightbulb from the basement.

Did I do something wrong or did you just hide my answer? I didn't look anything up.

 

[NPT]

I read the something where students were protesting about the following math question..."There are n sweets in a bag. Six of the sweets are orange. The rest of the sweets are yellow. Hannah takes a random sweet from the bag. She eats the sweet. Hannah then takes at random another sweet from the bag. She eats the sweet. The probability that Hannah eats two orange sweets is 1/3. Show that n²-n-90=0." I don't know what is so hard about that question.

 

[TheOriginalHappyGoat]

Did I do something wrong or did you just hide my answer? I didn't look anything up.

I hid your answer because you figured it out too fast.

 

[TheOriginalHappyGoat]

I read the something where students were protesting about the following math question..."There are n sweets in a bag. Six of the sweets are orange. The rest of the sweets are yellow. Hannah takes a random sweet from the bag. She eats the sweet. Hannah then takes at random another sweet from the bag. She eats the sweet. The probability that Hannah eats two orange sweets is 1/3. Show that n²-n-90=0." I don't know what is so hard about that question.

It is easy, but it's written in a very non-engaging way. Why not just ask, "How many sweets were there to start with?"

 

[larsIU]

Here's an interesting puzzle form today's Guardian. See if you can figure it out (don't give it away if you already know the answer).

There are three switches in the basement. One of them controls a single lightbulb in the attic. You are tasked with taking one trip to the basement, where you can flip the switches on and off as much as you like, and then taking one trip to the attic. After this one and only trip the attic, you have to figure out which switch controls the lightbulb. How do you do it?

To clarify, you cannot see the lightbulb from the basement.

How do we know if the light in the attic was "on" to begin with. This may not matter.

 

[TheOriginalHappyGoat]

How do we know if the light in the attic was "on" to begin with. This may not matter.

It doesn't matter. Just assume the light will be on if the proper switch in the basement is set to "on." They aren't toggle buttons. Just regular off-on switches. This isn't the kind of puzzle based on a trick of words. Nothing secretive about the setup.

 

[NPT]

It is easy, but it's written in a very non-engaging way. Why not just ask, "How many sweets were there to start with?"

I think they wanted to make you come up with the formula.... they really didn't ask how many sweets there were.

 

[TheOriginalHappyGoat]

I think they wanted to make you come up with the formula.... they really didn't ask how many sweets there were.

Sure they did. They are essentially asking you to solve for n, and that's what n is.

Math people are bad writers sometimes.