Brain teaser thread - Page 11

Immortal Wombat · October 27, 2002, 18:15

That's an encyclopedia?

Combat Ingrid · October 27, 2002, 18:20

For some of the people in this forum, sure

Lemmy · October 27, 2002, 18:26

Quote:

A bookworm eats from the first page of an encyclopedia to the last page.
The bookworm eats in a straight line.
The encyclopedia consists of ten 1000-page volumes and is sitting on a bookshelf in the usual order.
Not counting covers, title pages, etc., how many pages does the bookworm eat? Including the first and the last page.

Quote:

Follow the yellow line, please

That isn't from the first page to the last.

Dauphin · October 27, 2002, 18:28

It is the first and last page of the collection.

Combat Ingrid · October 27, 2002, 18:32

Quote:

Originally posted by Lemmy
That isn't from the first page to the last.

Yes it is

Go check for your self in your bookshelves

I'm off to bed now, if anyone cares about my riddle, you can find the answer in "The Hobbit".

JohnM2433 · October 27, 2002, 19:06

Quote:

Originally posted by Lemmy
That isn't from the first page to the last.

It's from the first page of the leftmost book to the last page of the rightmost book, because the way that books are arranged on a bookshelf, the first page of a book is on the right, and the last page is on the left (check and see). But books are typically arranged from left to right: for example, an encylopedia's "A" volume would be farthest to the left and it's "Z" volume farthest to the right. So when books are placed in a bookshelf in this fashion, the pages in a book increase in the opposite of the direction in which the books are ordered. How foolish I feel for not realizing that!

I thought I must be missing something, because the problem seemed too easy. But I guess that it's one of those things most people don't think of, which is what makes it a good riddle. Still, even thinking that this was probably a trick problem, I couldn't figure it out...

Jaguar · October 27, 2002, 20:14

Gollum! Gollum! The answer is dark, of course!

I remembered the riddle!!

Skanky Burns · October 27, 2002, 20:20

So, wheres your puzzle?

Jaguar · October 27, 2002, 20:21

Here's an easy one

Ten people wrote down their names on one slip of paper each. Then everybody put the slip of paper with their name into a hat. Everyone then drew one of the ten pieces of paper from the hat. What is the probability that exactly 9 people recieved the peice of paper with their name on it?

Dauphin · October 27, 2002, 20:30

0%

Jaguar · October 27, 2002, 20:31

yep

Jaguar · October 27, 2002, 20:35

I have some more good ones, so if someone doesn't want to post one, I'll post one.

Jaguar · October 27, 2002, 20:46

OK its been ten minutes so I'll go ahead and post one. SD should still post something, though, so I have something to solve.

square root(x+sqrt(x+sqrt(x+sqrt...)))=2
find x

If someone could make a neater version it would be appreciated. I don't know how.

Hint: the answer is not messy.

Method · October 27, 2002, 20:54

i think i know, but, fearing having to post a brain teaser myself (of which i have none), i'll withold my answer

Jaguar · October 27, 2002, 21:00

I'll post another one. Go ahead.

Method · October 27, 2002, 21:06

1?
EDIT: no...that's not it...

Dauphin · October 27, 2002, 21:14

Quote:

Originally posted by Jaguar Warrior
OK its been ten minutes so I'll go ahead and post one. SD should still post something, though, so I have something to solve.

square root(x+sqrt(x+sqrt(x+sqrt...)))=2
find x

If someone could make a neater version it would be appreciated. I don't know how.

Hint: the answer is not messy.

2

Dauphin · October 27, 2002, 21:16

Five suspects were rounded up in connection with a robbery. Their statements were as follows:

Alex: "Chris and Dave are lying."
Brad: "Alex and Eric are lying."
Chris: "Brad and Dave are lying."
Dave: "Chris and Eric are lying."
Eric: "Alex and Brad are lying."

Who is the only suspect you know with certainty to be lying?

Jaguar · October 27, 2002, 21:18

Yep. Did you guess? Or did you square both sides and substitute?

Dauphin · October 27, 2002, 21:22

Quote:

Originally posted by Jaguar Warrior
Yep. Did you guess? Or did you square both sides and substitute?

Given that its an infinite series the figure inside each of the SQRT() must be equal to x. Therefore x = SQRT() = 2

Dauphin · October 27, 2002, 21:28

More accurately..

square root(x+sqrt(x+sqrt(x+sqrt...)))= A

x = A * (A-1)
.. = 2 *1
.. = 2

Urban Ranger · October 28, 2002, 02:57

Quote:

Originally posted by Ignorance
r = rate of falling snow (unknown)
ts = when snow has started falling (which we want)
p = plows constant rate of removing snow (unknown)

snow depth at time t: s = r*(t-ts)
speed of plow: v = p/s
which gives us v = p/(r*(t-ts))

v is not right. p should be in a unit like m³/s. Divide that by s, which should be in metres, gives a unit in m²/s, which isn't speed.

monolith94 · October 28, 2002, 04:00

Alex is lying

monolith94 · October 28, 2002, 04:51

If alex is telling the truth, then dave is lying. If dave is lying then chris must be telling the truth. However, alex already said that chris was lying. Therefore alex must be a certain LIAR!

Urban Ranger · October 28, 2002, 05:04

Not necessarily. Just because Dave is lying doesn't mean Chris isn't lying.

Dauphin · October 28, 2002, 10:32

Quote:

Originally posted by monolith94
If alex is telling the truth, then dave is lying. If dave is lying then chris must be telling the truth. However, alex already said that chris was lying. Therefore alex must be a certain LIAR!

Right answer, wrong reasoning.

Rogan Josh · October 28, 2002, 10:49

Quote:

Originally posted by Sagacious Dolphin
Five suspects were rounded up in connection with a robbery. Their statements were as follows:

Alex: "Chris and Dave are lying."
Brad: "Alex and Eric are lying."
Chris: "Brad and Dave are lying."
Dave: "Chris and Eric are lying."
Eric: "Alex and Brad are lying."

Who is the only suspect you know with certainty to be lying?

Alex is lying.

Let us assume he is telling the truth. Then Chris and Dave are lying.

Chris lying -> one of Brad or Dave must be telling the truth, but we have already said that Dave is lying, so Brad must be telling the truth.

But Brad claims Alex is lying!

Therfore we have a logical contradiction, so Alex must be lying.

Rogan Josh · October 28, 2002, 10:54

Quote:

Originally posted by Sagacious Dolphin
More accurately..

square root(x+sqrt(x+sqrt(x+sqrt...)))= A

x = A * (A-1)
.. = 2 *1
.. = 2

Incidentally I would have done this by writing

A= sqrt(x+sqrt(x+sqrt...))=sqrt(x+A)
So
A^2=x+A
x=A^2-A=4-2=2

Dauphin · October 28, 2002, 10:57

I'll post another...easier one.

A hotel has 1,000 rooms numbered 1 to 1,000. Jack is looking after the hotel for the winter and is going slightly crazy. He decides to flick every roomlight switch in the hotel. He then decides to flick the switch in every other room (starting with room 2). He then flicks the switch in every third room (starting with room three). He then flicks the switch in every fourth room (starting in room 4).

If all lights were originally off, which lights remain on once Jack has finished switching every 1,000^th roomlight switch?

Dauphin · October 28, 2002, 10:58

Oops you got it right whilst I was composing another. Well done.

Can you also proove that you can't determine if the others are lying?