Brainteaser

Roboframer · Post by **Roboframer** » Thu 27 Dec, 2007 9:37 pm

Was going to put this here and TFG - did TFG - took so long to format that I can't be bothered to do both - so here's the link

(Edit - it's in 'Warped' - so you have to be registered - sorry!)

Moglet · Post by **Moglet** » Thu 27 Dec, 2007 11:14 pm

Blimey, Robo - finally lost my Grumble virginity over these....

Moglet · Post by **Moglet** » Thu 03 Jan, 2008 7:44 pm

Here's another couple of brainteasers:

Teaser 1:

You are in front of a room with a closed door, but no windows. Inside the room are three lightbulbs. Outside the room are three switches. Each of the three switches operates one of the lightbulbs. You can turn the switches on and off as many times as you like, but you can only open the door once. How do you determine with 100% certainty which light is connected to which switch?

Teaser 2:

A fridge is in a completely sealed room. The fridge is plugged in, and switched on. The door of the fridge is open. Will the room:

a) get colder?
b) stabilise at a constant temperature?
c) get warmer?

What is the reasoning behind your answer?

Bill Henry · Post by **Bill Henry** » Thu 03 Jan, 2008 9:54 pm

1) Since you’re in front of a room (not in a room), open the door.

Turn on one switch. Look in the room and see which light goes on. Keep the door open.

Turn on another switch. Look in the room and see which light goes on. Keep the door open.

If you have a bad memory, check the last switch to verify that the last light goes on. Close the door and do something useful.

2) The room will stabilize. In order for the interior of ‘fridge to get cold, a compressor motor has to do its thing. That generates heat. So, both heat and cold gets pumped into the room. With the door open, the compressor will be working overtime and burn itself out eventually. So, without both heat and cold, the room will stabilize.

Moglet · Post by **Moglet** » Thu 03 Jan, 2008 10:01 pm

Oops! Forgot a vital condition.

Once you open the door, you can't touch any of the switches again!

Also, on Teaser 2, assume that there will be no failures of mechanical or electrical systems.

Roboframer · Post by **Roboframer** » Thu 03 Jan, 2008 10:06 pm

Moglet wrote:Oops! Forgot a vital condition.

Once you open the door, you can't touch any of the switches again!

Why not - this is a free country - I am outraged!

(Because opening the door immobilises the switches)

Oh - OK!

Moglet · Post by **Moglet** » Thu 03 Jan, 2008 10:16 pm

Roboframer wrote:...this is a free country...

Since when?

Bill Henry · Post by **Bill Henry** » Thu 03 Jan, 2008 10:16 pm

Moglet wrote:Oops! Forgot a vital condition.

Once you open the door, you can't touch any of the switches again!

Oh, right, just when you figure it out, the rules change.

No fair!

Moglet · Post by **Moglet** » Thu 03 Jan, 2008 10:20 pm

My sincere apologies, Bill!

Roboframer · Post by **Roboframer** » Thu 03 Jan, 2008 10:24 pm

I had Bill's answer but knew it was too easy.

Are you allowed to drill a hole through the door? - That's what I did to find out if my fridge light goes out when I close the door.

Moglet · Post by **Moglet** » Thu 03 Jan, 2008 10:27 pm

Roboframer wrote:Are you allowed to drill a hole through the door? - That's what I did to find out if my fridge light goes out when I close the door.

Ok. Pedantry time. One may only view the interior of the room once. Once one looks inside the room (by whatever creative means!) one may no longer change the switch settings.

w00dward · Post by **w00dward** » Thu 03 Jan, 2008 10:44 pm

Can you look through the hole while throwing the switches?

I've either got painting the bulbs or wiring cats up to them and just listening to which cat is getting a tingle.

As for the fridge question, is my beer in it?

Roboframer · Post by **Roboframer** » Thu 03 Jan, 2008 10:51 pm

OK I have the bulb/switch one - but I'm just going to give a clue.

Mrs R called me earlier to change a spotlight in the living room - 4 spots on an 'S' shaped rod on the ceiling.

Didn't tell me it had just popped and I never realised either - when they do that they normally trip the fuse.

Burned my hand.

Moglet · Post by **Moglet** » Thu 03 Jan, 2008 10:57 pm

w00dward wrote:Can you look through the hole while throwing the switches?

Again I say, once lookey lookey, no switchy switchy!!!

w00dward wrote:As for the fridge question, is my beer in it?

Any more anti-feline comments, Woody, and I'm confiscating your ale supplies until further notice!

Bill Henry · Post by **Bill Henry** » Thu 03 Jan, 2008 10:59 pm

What are three light switches doing on the outside of a refrigerator door?

Moglet · Post by **Moglet** » Thu 03 Jan, 2008 11:01 pm

You're just determined to make a grown woman cry, Bill...

w00dward · Post by **w00dward** » Thu 03 Jan, 2008 11:06 pm

Moglet wrote: Any more anti-feline comments, Woody, and I'm confiscating your ale supplies until further notice!

That is a severe punishment for such a minor offense. No cat is worth my beer! Well, unless it can get the beer from the fridge, open it and pour! Only then would I reconsider.

How energy efficient is the fridge? If its A rated the room will cool, its it E rated it'll warm up because the motor is running too hot.

Roboframer · Post by **Roboframer** » Thu 03 Jan, 2008 11:16 pm

I think the clue is in the sealed room.

It's not sucking air from the outside, like an aircon unit - energy is being produced - that energy comes from the outside though, and cannot get back out.

The room heats up.

Bill Henry · Post by **Bill Henry** » Fri 04 Jan, 2008 4:23 pm

Moglet wrote:You're just determined to make a grown woman cry, Bill...

Ah, then my work is done!

Moglet · Post by **Moglet** » Fri 04 Jan, 2008 6:26 pm

Just call me "Squonk" from now on, Bill.