# The Naked Scientists Forum

### Author Topic: Riddle  (Read 6479 times)

#### Laith

• Sr. Member
• Posts: 164
##### Riddle
« on: 20/04/2006 23:24:30 »
If there were two separate rooms, one with 3 switches (where you are standing) and one with 3 light bulbs, you are allowed only one entry in the other room, how could you find out which switch belongs to which light bulb?

Laith
« Last Edit: 21/04/2006 09:12:58 by Laith »

#### wim

• Full Member
• Posts: 66
##### Re: Riddle
« Reply #1 on: 20/04/2006 23:54:32 »
You put one of the three switches on for about 1 minute, switch it off, put on an other switch and enter the room, the bulb that is giving light was the one you switched on last. The bulb that is still warm is the one you switched on first and the third can be easily figured out because you know the other two.

grtz

#### another_someone

• Guest
##### Re: Riddle
« Reply #2 on: 21/04/2006 00:17:59 »
quote:
Originally posted by Laith

If there were two separate rooms, one with 3 switches (where you are standing) and one with 3 light bulbs, you are allowed only one entry in the other room, how could you find out witch switch belongs to witch light bulb?

It depends upon what resources you have to hand.

By switching one of the switches on, and going into the other room, you can tell which light one of the switches controls; so the only issue is to differentiate between the other two.

If you can see if the room is lit (whether by leaving the door open, or seeing the light seeping around the door), then it is a matter of removing one of the other two light bulbs, and then switching on the other two switches in sequence, and see which lights up the room, and which does not light up the room.

Failing that, you could remove one of the light bulbs, and replace it with metal strip or wire, and turn on the switches, and determine which switch causes the fuse to blow.

If you have the right kit available, you could simply leave one light bulb removed, and use a continuity tester to test which switch was connected to an open circuit.

Another possibility (if they are incandescent light bulbs) would be to switch one light bulb on, wait a long time for it to properly warm up, then switch the light bulb off, and switch another light bulb on, then enter the room, and observe which light bulb is illuminated (that is connected to the switch you have just switched on), which is dark but still warm (that is connected to the switch you recently switched off), and which is dark and cold (that is connected to the switch you had not switched on at all).

George

#### Laith

• Sr. Member
• Posts: 164
##### Re: Riddle
« Reply #3 on: 21/04/2006 03:50:37 »
Okay that was easy for you guys, here's another one:

There are 2 roads, one going east and one going west, and only one of them leads to the right place. There is a house in the middle with 2 people inside; one only speaks the truth and one only lies, How can you know which direction to take if you only can ask one question?
(you dont know who will answer the door)

Laith
« Last Edit: 21/04/2006 15:54:44 by Laith »

#### another_someone

• Guest
##### Re: Riddle
« Reply #4 on: 21/04/2006 04:11:15 »
quote:
Originally posted by Laith

Okay that was easy for you guys, here's another one:

There are 2 roads, one going east and one going west, and only one of them leads to the right place. There is a house in the middle with 2 people inside; one only speaks the truth and one only lies, How can you know witch direction to take if you only can ask one question?
(you dont know who will answer the door)

Laith

Sorry, a variation on exactly the same puzzle has been asked before:

http://www.thenakedscientists.com/forum/topic.asp?TOPIC_ID=3781

quote:
Originally posted by harryneild

Ok lets see if the brain boxes of this forum know the answer to this puzzle!

You have died and before heaven there are two identical doors. In front of each door there is a guard. Both guards are identically looking. The one guarding the door to heaven will always tell the truth. The one guarding the door to hell will always lie. If you can ask them 1 question which they both answer, in order to find out which door is which, what do you ask them?
Harry Eakins

"Knowledge has to be improved, challenged, and increased constantly, or it vanishes." Peter F. Drucker

quote:
Originally posted by another_someone

It is an old question, with a number of variations.

The solution is fairly straight forward.

Regard the two guards as logic circuits, one will invert the answer, and the other will give a positive result.  If you feed a response through both circuits, you will get a single negation (this is true no matter which order the response passes through).

Thus you ask one guard what the other guard would have said (thus, either the first guard will invert the answer, and the second will just pass the answer through; or the first guard will pass the answer through, and the second will invert the answer; in either case you know the answer will have been inverted only once).

This if you ask one guard to tell you what answer the other guard would have told you, you know that the answer you will get is the exact inverse of the truth.

George

Do you wish me to rephrase the same answer to reflect the very slight difference in nomenclature between the two questions?

George

#### Laith

• Sr. Member
• Posts: 164
##### Re: Riddle
« Reply #5 on: 21/04/2006 05:02:02 »
Damn!

Alright I'm guessing you know this one too

Divide this into 4 identical shapes

Laith

#### Laith

• Sr. Member
• Posts: 164
##### Re: Riddle
« Reply #6 on: 21/04/2006 05:03:25 »
Anyone has more puzzles?
maybe harder ones? haha

Laith

#### another_someone

• Guest
##### Re: Riddle
« Reply #7 on: 21/04/2006 11:47:31 »
quote:
Originally posted by Laith

Damn!

Alright I'm guessing you know this one too

Divide this into 4 identical shapes

Laith

OK:

Draw a line from the top left corner to the bottom right corner.

Draw another line from the inside corner to the corner at the bottom left.

You now have 4 triangles.

The triangle on the bottom has a baseline of 2, and a height of 1 (and the two remaining sides are of approximately 1.4 in length).

The triangle on the left, if rotated counter-clockwise by 90 degrees, also has a baseline of 2 and a height of 1.

The two remaining triangles are right angle triangles, where the two shorter sides are of length 1, and the remaining side is about 1.4 in length.

You then bring the two smaller triangles together to form a larger triangle of a height of 1, a baseline of 2, and the remaining sides of about 1.4.

George

#### Carolyn

• Neilep Level Member
• Posts: 3761
##### Re: Riddle
« Reply #8 on: 21/04/2006 15:39:12 »
I'm not feeling very creative, so here's an easy one.

Two coins equal .30 cents.  One of them is not a nickel.  What are the two coins?

Carolyn

#### Laith

• Sr. Member
• Posts: 164
##### Re: Riddle
« Reply #9 on: 21/04/2006 15:44:20 »
quote:
Originally posted by another_someone

You then bring the two smaller triangles together to form a larger triangle of a height of 1, a baseline of 2, and the remaining sides of about 1.4.

George

This gives us 3 not 4 Identical shapes

Laith
« Last Edit: 21/04/2006 15:48:19 by Laith »

#### Laith

• Sr. Member
• Posts: 164
##### Re: Riddle
« Reply #10 on: 21/04/2006 15:49:35 »
quote:
Originally posted by Carolyn

One of them is not a nickel.

Carolyn

but the other one could be a nickel, is that it?

Laith

#### Carolyn

• Neilep Level Member
• Posts: 3761
##### Re: Riddle
« Reply #11 on: 21/04/2006 16:08:33 »
I told you it was easy.

Carolyn

#### Laith

• Sr. Member
• Posts: 164
##### Re: Riddle
« Reply #12 on: 21/04/2006 16:17:33 »
Thanks Carolyn, if you remember other ones please post them

Laith

#### another_someone

• Guest
##### Re: Riddle
« Reply #13 on: 21/04/2006 18:24:30 »
quote:
Originally posted by Laith

quote:
Originally posted by another_someone
You then bring the two smaller triangles together to form a larger triangle of a height of 1, a baseline of 2, and the remaining sides of about 1.4.

This gives us 3 not 4 Identical shapes

Sorry - I must learn to read the question correctly

OK, you really have not given many restraints upon what one can do to create the 4 shapes; so, if I were to take a few liberties, and accept integrity the lines you have drawn, but not the integrity of the space contained therein, I would propose the following simple answer:

Take an axis from the corner at the centre to to the corner at the centre right.

Mirror translate the two short lines that form the inner corner, so that they now form the outer corner of a square in the upper right of a square.

You may now divide this square into four.

The other possibility would be:

Divide the shape into 3 smaller squares of 1 unit on each side.

Subdivide each of these 3 squares into 4 smaller squares of ½ unit on each side.

Combine 3 of each of these smaller squares into 4 L shapes that mirror the original shape, but are only half the dimensions of the original shape.

George

#### Laith

• Sr. Member
• Posts: 164
##### Re: Riddle
« Reply #14 on: 21/04/2006 18:57:06 »
quote:
Originally posted by another_someone

Combine 3 of each of these smaller squares into 4 L shapes that mirror the original shape, but are only half the dimensions of the original shape.

George

Right
Here is how it looks like

Laith

#### The Naked Scientists Forum

##### Re: Riddle
« Reply #14 on: 21/04/2006 18:57:06 »