Quiz - Mind Trap

BigRed · Post by **BigRed** » 7 Dec 2003, 09:59

It's a stupid answer

I dont think any one will get it unless they have read it before....
Think about it being a stupid answer and u might get it...

zworqy · Post by **zworqy** » 8 Dec 2003, 14:01

Maybe for attempting to commit suicide then...?

jw · Post by jw » 8 Dec 2003, 15:39

something in the words "shady" and "shadow" ?

chux · Post by **chux** » 8 Dec 2003, 23:27

Nope, theyre the names they use in Mind Trap...

Im thinking him being unconcious could mean he's asleep...so maybe he has a job that is dangerous to be asleep on...pilot maybe...
But thats not outside the Jewellers

Revolt · Post by **Revolt** » 9 Dec 2003, 00:34

no

if u want a hint just ask

BigRed · Post by **BigRed** » 9 Dec 2003, 01:51

Hint: It was something that the people that saw it happen told Shadow...
Keep guessing and here's another one...

Shadow was on holiday on the aisle of Begile. this is an Island where the natives always lie and the visitors always tell the truth. Shadow was walking through a mall when Bill, Frank, and Joe approached him. Joe said, "All of us are natives." Frank said, "Only one of us is a visitor." Who is a visitor."

zworqy · Post by **zworqy** » 9 Dec 2003, 10:02

BigRed wrote:Shadow was on holiday on the aisle of Begile. this is an Island where the natives always lie and the visitors always tell the truth. Shadow was walking through a mall when Bill, Frank, and Joe approached him. Joe said, "All of us are natives." Frank said, "Only one of us is a visitor." Who is a visitor."

Frank

Here's a stupid thought on the previous one: Shady tried to break into to the Jewellers shop, but the brick he threw bounced on the reinforced glass... LOL

Revolt · Post by **Revolt** » 9 Dec 2003, 10:11

zworqy wrote:
Here's a stupid thought on the previous one: Shady tried to break into to the Jewellers shop, but the brick he threw bounced on the reinforced glass... LOL

that's a stupid enough answer to be right

yer he threw a brick or rock and it bounced back and hit him in the head, turing him uncouncious

zworqy · Post by **zworqy** » 9 Dec 2003, 12:13

LOOOOOOOOOOOL!!!!

But was Frank the visitor?? (ye he was

)

chux · Post by **chux** » 9 Dec 2003, 15:53

You dont get arrested for 'attempted burglary'...
It makes sense for Fred to be the visitor...

zworqy · Post by **zworqy** » 9 Dec 2003, 21:34

chux wrote:You dont get arrested for 'attempted burglary'...

You don't? What anarchy country do you live in?

chux wrote:It makes sense for Fred to be the visitor...

LOL, ther wasn't even a Fred...

BigRed · Post by **BigRed** » 10 Dec 2003, 03:39

chux wrote:It makes sense for Fred to be the visitor...

LOL, ther wasn't even a Fred...

[/quote]
Yes their is.... and he is the visitor.

Vaitork · Post by **Vaitork** » 10 Dec 2003, 05:07

Wasn't it Frank?

zworqy · Post by **zworqy** » 10 Dec 2003, 08:13

There was no Fred, just Joe, Frank, and Bill. Joe is obviously lying, so he's a native. If Frank is lying, he's a native and the other two are visitors, but Joe was a native, so that's not right. Hence Frank is telling the truth and is the only visitor!

chux · Post by **chux** » 10 Dec 2003, 12:02

Hehe, Fred, Frank, y'know...

I live in anarchist UK...I dont think you get arrested for knocking yourself out with a brick...maybe im wrong

djacosmo · Post by **djacosmo** » 11 Dec 2003, 12:21

can i take a wild guess and say that shadow was the guest.

Drew

zworqy · Post by **zworqy** » 11 Dec 2003, 12:36

djacosmo wrote:can i take a wild guess and say that shadow was the guest.

Drew

He he... good point! HE is obviously a visitor too, but of the threee others, it was Frank.

Jalli · Post by **Jalli** » 13 Dec 2003, 02:10

1: You got two ropes and one lighter. If you light a rope in one end it takes a minute untill it is all burnt up. However the speed of burning is not linear. That means that when 30 seconds has gone it is not necessarily that half the rope has been burnt. How can you measure 45 seconds using these tools?

2: How many zeroes are there in the end of 1000! ?

3: Teofilus has 2 children. At least one of them is a girl. What is the probability that the other one is a girl as well?

4: Imagine you are on a tvshow. You have an option to choose door A, B or C. Behind one of them is a car. Lets say you choose A. Then the host opens door C and you see that that one is empty. You are now given a choice wether you want to keep A or change to B. What is the smartest thing to do by thinking probability? Pliz explain and don't just guess...

Vaitork · Post by **Vaitork** » 13 Dec 2003, 02:26

Jalli wrote:2: How many zeroes are there in the end of 1000! ?

Just one, right?

ToTaL · Post by **ToTaL** » 13 Dec 2003, 02:32

A 4: If the host open the 3rd door after u choose 1, it's to make u think one more time " have I done the right choice ". In some of the cases the you will take door B instead of A. Thats what i think.
Rather stick with A.

jw · Post by jw » 13 Dec 2003, 02:52

3: 1/3 if there is the same change to have: m+w, w+w, m+m or w+m (m = man, w = woman) and at least one is w, than only in one of the three cases with at least one woman the other one is a woman aswell
4: change to door b, when u made your choise for a, it was 1/3 chance, if u choose b now you will have 2/3, you think maybe not, if you stick to a you have 1/2 and if you go to b you have also 1/2 now, but:
if you chose a and it is b, the host opens c and you should change
if you chose a and it is c, the host wouldn't open c, but b and you should change to c
if you chose a and it is a, the host could open b or c and you shouldn't change
so there are 2 out of 3 times where it is better to change, so take b

MagnusB · Post by **MagnusB** » 13 Dec 2003, 02:53

Jalli wrote:4: Imagine you are on a tvshow. You have an option to choose door A, B or C. Behind one of them is a car. Lets say you choose A. Then the host opens door C and you see that that one is empty. You are now given a choice wether you want to keep A or change to B. What is the smartest thing to do by thinking probability? Pliz explain and don't just guess...

Spoiler for this one, interesting read too: http://www.straightdope.com/classics/a3_189.html

chux · Post by **chux** » 13 Dec 2003, 13:36

I didnt read Mag's link...yet

1: Count instead...

2: None, theres a !

3: 50:50, it doesnt matter what he had before, its half and half between girl/boy...jw's theory makes sense, and I cant see where he would have gone wrong...but i dont like it...

EDIT: Mwahaha... okii, for those 4 possible cominations (MM, MW, WM, WW), we can eliminate MM. Then we have MW, WM, and WW. This is where jw says its 1/3.
As everyone here can see, WM and MW are THE SAME, leaving only one of those and WW...so it IS 1/2 or 50% or whatever.
The gender of one kid cant affect the gender of another.

4: Stick with A. Obviously the guy opened C because it was wrong, and being a TV show, he wants you to be entertaining, eg: choosing the wrong door after having it right in the first place. So all he's really doing is giving you another chance to choose. So if my theory is right, he's trying to make you go wrong...

Vaitork · Post by **Vaitork** » 13 Dec 2003, 19:25

Vaitork wrote:
Jalli wrote:2: How many zeroes are there in the end of 1000! ?
Just one, right?

Whoa!!! It's a factorial calculation

I'm technically correct though.. The last number is a zero bcuz of 10, 20, 30.. 100 and all the numbers ending in zero.. But if you want ALL the zeros then... mmm... err... uhm... lemme think

Vaitork · Post by **Vaitork** » 13 Dec 2003, 19:30

2: Two hundred?

zworqy · Post by **zworqy** » 13 Dec 2003, 23:26

Jalli wrote:1: You got two ropes and one lighter. If you light a rope in one end it takes a minute untill it is all burnt up. However the speed of burning is not linear. That means that when 30 seconds has gone it is not necessarily that half the rope has been burnt. How can you measure 45 seconds using these tools?

2: How many zeroes are there in the end of 1000! ?

3: Teofilus has 2 children. At least one of them is a girl. What is the probability that the other one is a girl as well?

4: Imagine you are on a tvshow. You have an option to choose door A, B or C. Behind one of them is a car. Lets say you choose A. Then the host opens door C and you see that that one is empty. You are now given a choice wether you want to keep A or change to B. What is the smartest thing to do by thinking probability? Pliz explain and don't just guess...

1. You can't...

2. One

3. This is a very interesting one! I've read it in magazine, and apparently jw's theory is the right answer. But no matter how much I think about it, I can't accept anything else than that it must be 1/2!! The question clearly ask for the sex of the other child, the one who wasn't necessarily a girl. Thus, the girl has nothing to do with the question. And what gender a child is is obviously 50/50

4. You should change. The host would obviously not choose the door with the car, so the probability that the car is behind the last door is thus higher.

zworqy · Post by **zworqy** » 14 Dec 2003, 12:19

zworqy wrote:1. You can't...

OK, I take that back now... I've figured it out tonight (in my sleep

)

Fold one of the ropes so you get the two ends together. Ignite them both at the same time. Since the rope will now burn at double speed, It will burn in 30 seconds.

Fold the other rope "into four" so you get both ends and a "curve" together. Ignite all this and the "curve" will break into two, and the rope will burn with 4 times speed -> 15 seconds.

So, if you ignite one of these ropes exactly when the other one burns up, it will take totally 45 SECONDS to burn them both.

Jalli · Post by **Jalli** » 14 Dec 2003, 13:05

jw got 3 and 4 first. The two first remains unsolved as far as I can see. Zworqys solution has a small error I think. I think u suddenly have too many ropes that doesn't burn at same speed and aren't connected to eachother...

chux · Post by **chux** » 14 Dec 2003, 14:36

What!??!?!!?
jw was completely wrong!
he says that 3) is 1/3 because of his MW WW WM theory, if you read my post you'll realise that thats bullplop...MW and WM are the same, and having a girl doesnt mean its more likely that you'll have a boy next, thats not how genetics work.

as for his 4), when the guy opens the door, he is technically starting a new game, seeing as hes giving you the choice to change again and everything. therefore, the chances of A being right are 1 in 2. obviously because there is one right door out of two possible doors!
The ratio before C being opened makes no difference to the final result.
"4: change to door b, when u made your choise for a, it was 1/3 chance, if u choose b now you will have 2/3" - Why does B change but not A?

If people listen I'll gladly take a couple of points for my efforts

jw · Post by jw » 14 Dec 2003, 14:54

dear chux,

the point in the question about the kids is "he has two kids"
the first kid is 50/50 change for getting a boy or a girl
so the first can be a boy or a girl

for the second kid the change is 50/50 again
so if he got a girl first he can get a girl again or a boy, if the first was a boy he can now get girls or a boy again.

so there is the same change in having a girl and a girl again, a girl and than a boy, a boy and a girl or two boys.

I hope you agree that those 4 options have the same change. Ok, now he has two kids, but at least one is a girl, this means there is the same change in having a girl first and than a boy, two girls or first a boy and a girl after that.

only in 1 of these 3 cases the second is a girl again!

If the question was the first child is a girl, what is the change in having a girl again, than the answer would be 1/2

and for question 4, read this link posted by MagnusB: http://www.straightdope.com/classics/a3_189.html

Phillip · Post by **Phillip** » 14 Dec 2003, 15:44

Jalli wrote:1: You got two ropes and one lighter. If you light a rope in one end it takes a minute untill it is all burnt up. However the speed of burning is not linear. That means that when 30 seconds has gone it is not necessarily that half the rope has been burnt. How can you measure 45 seconds using these tools?

Obviously, if you light one rope in both ends, it burns in 15 seconds. The solution must be: light one rope in both ends, then when it has burned up light the second rope in one end. When the last rope burns out, 45 seconds has passed...

Jalli wrote: 2: How many zeroes are there in the end of 1000! ?

Let's see, on the end of 1000 is 0, that's one zero...

Jalli · Post by **Jalli** » 14 Dec 2003, 16:08

Phillip, one rope burns for 1 min, not 30 secs...

And on 2 I don't mean "END" like that, but all the following zeroes in end.

jw · Post by jw » 14 Dec 2003, 17:21

Jalli, the speed of burning is not linear, but is the accellaration of the speed linear?

Jalli · Post by **Jalli** » 14 Dec 2003, 17:35

Not necessarily

Vaitork · Post by **Vaitork** » 14 Dec 2003, 18:19

Jalli wrote:And on 2 I don't mean "END" like that, but all the following zeroes in end.

Am I even close with 200?

Phillip · Post by **Phillip** » 14 Dec 2003, 18:24

Jalli wrote:Phillip, one rope burns for 1 min, not 30 secs...

Oooops! My mistake

Got to think a little bit more then...

Phillip · Post by **Phillip** » 14 Dec 2003, 18:29

How about this:

Light the first rope in both ends, and the second rope in one end. When the first rope burns out, light the second one in the other end. This would be 45 secs!

zworqy · Post by **zworqy** » 14 Dec 2003, 21:36

Jalli wrote:Zworqys solution has a small error I think. I think u suddenly have too many ropes that doesn't burn at same speed and aren't connected to eachother...

WTF!!???

My solution was perfectly alright!! If it helps you can think of it like this:
roll the "15-sec" tope into a coil with 2 laps. Then burn off both laps (where the ends meet). Then the rope will burn from 4 directions, e.g. in 15 seconds.

Vaitork · Post by **Vaitork** » 14 Dec 2003, 23:13

Jalli wrote:2: How many zeroes are there in the end of 1000! ?

Ohh ohh ohhhhhhh

199

is it?

Jalli · Post by **Jalli** » 14 Dec 2003, 23:36

Phillip got the rope one. I also has recieved the correct answer to task 2 on IRC today. I won't tell who, but if you whane beat him you must solve it b4 he posts.

jw · Post by jw » 15 Dec 2003, 01:46

I think Philips one only works when the speed of burning is linear....

zworqy · Post by **zworqy** » 15 Dec 2003, 14:22

Jalli wrote: 2: How many zeroes are there in the end of 1000! ?

Code: Select all

Formula Amount Range:
10*9    90     10-990
2*9     18     100 - 900
9*9     81	  101-909.
3        3	  1000.

Sum:	192

...or 193 if you start with a 0

Jalli · Post by **Jalli** » 15 Dec 2003, 15:18

jw wrote:I think Philips one only works when the speed of burning is linear....

Nope, it works anyway. Lighting fire to both ends of rope means that it will burn out in 30 secs. Since he lit the second rope at the same time, 30 secs will have passed on that rope and 30 secs will remain. (I'm not talking lengths here) By then lighting the other side of the "30-secondrope" it will take 15 secs till they meet and 45 seconds has passed.

Phillip · Post by **Phillip** » 15 Dec 2003, 15:52

Jalli wrote:2: How many zeroes are there in the end of 1000! ?

Ok, here we go:

1000! = 1000 * 999 * 998 * 997 * 996 * ... * 2 * 1

This equals some number followed by a number of zeroes:

(some number) * 10 * 10 * 10 * 10 * .... * 10

Now the question is how many 10's are there at the end?
It can be rewritten like this, using 10 = 5 * 2:

1000! = B * 5 * 5 * 5 * ... * 2 * 2 * 2
(where B is some other number which cannot be divided by 5 or 2)

When you multiply all the numbers from 1 to 1000, you get an awfull lot of 2's, more than 500 actually. It is quite obvious that we get more 2's than 5's. Now we want to know the number of pairs of 5's and 2's, it's enough to count the 5's. How many are there?

From every fifth number we get one 5:

5 * ... * 10 * ..... * 15

This gives us 1000 / 5 = 200 fives

However, every 25th number gives us an extra five in the product, and every 125th number gives us even one more 5 and so on. If we count these, we get:

1000 / 5 = 200
1000 / 25 = 40
1000 / 125 = 8
1000 / 625 = 1.XX (gives 1 extra five)

The sum is 249.

So, 1000! is a number followed by 249 zeroes

Jalli, or anyone else, can you solve this:

Can you give me n following numbers, of which none are primes?
That is, find a number A such that:

A + 1, A + 2, A + 3, ..., A+ n
are not primes?

Phillip

jw · Post by jw » 15 Dec 2003, 16:11

Jalli wrote:
jw wrote:I think Philips one only works when the speed of burning is linear....
Nope, it works anyway. Lighting fire to both ends of rope means that it will burn out in 30 secs.

anyway?
the rope could be 37,5 centimeters for example. if the burning is not linear this could mean the first 10 seconds will burn 2,5 cm, the next 10 seconds it will go faster (because the rope got warm and is burning faster now) and there will burn 5 cm, so after 20 seconds 7,5 cm burned. but after 20 seconds the speed is max and the rope is burning at constant speed of 7,5 cm/minute. so after 60 seconds 37,5 cm has burned.
if you now lit the rope at both ends the first 10 seconds will burn 5 cm (2,5 cm at both ends) the next 10 seconds there will burn 10 cm (5 at both sites) so after 20 seconds 15 cm has burned. for now on there will burn 15 cm per 10 seconds (7,5 cm at both ends). so the rope will burn for 15 more seconds. this means it will burn out in 35 seconds in stead of 30 seconds.

jw · Post by jw » 15 Dec 2003, 16:21

Phillip wrote:Can you give me n following numbers, of which none are primes?
That is, find a number A such that:

A + 1, A + 2, A + 3, ..., A+ n
are not primes?

A = 3,2123
A + 1 = 4,2123 is not a prime
A + 2 = 5,2123 is not a prime
A + 3 = 6,2123 is not a prime
A + 4 = 7,2123 is not a prime
A + 5 = 8,2123 is not a prime
A + n = n +3,2123 is not a prime

if A have to be a whole number you would like to find a real lot of following numbers that are not primes, so you would need the biggest prime number...
hmm, if you know the biggest prime number you may tell me and mail me the proof for it

Jalli · Post by **Jalli** » 15 Dec 2003, 16:22

Warmth has nothing to do with it. It won't burn in same place in two different speeds depending on which way you go.

Btw: A = http://mersenne.org/prime6.txt

jw · Post by jw » 15 Dec 2003, 16:56

Jalli wrote:Warmth has nothing to do with it. It won't burn in same place in two different speeds depending on which way you go.

not depending in which way you go, but the speed doesn't have to be linear and if the accellaration isn't linear to, it doesn't have to be 30 seconds.

it could be that the burningproces has to "start up" if the speed is not linear this can be. normaly you have this "start up" ones, but if you light it up at two sites you have it twice and burning the rope will take over 30 seconds. now you can have two different speeds at one places, because if the burning starts at one side that is slower than when the burnig get there at full speed.

look at this, if the burning produce more warmth (energy/ whatever) than the lighter, the burning will light the next part of the rope faster than the lighter, i can't explain this better in english, but i hope you understand.

jw · Post by jw » 15 Dec 2003, 17:04

Jalli wrote:A = http://mersenne.org/prime6.txt

you mean A could be: (2^20996011)-1
but i'm sure there is a bigger prime and it will be found

really cool site btw, took me 115,92 seconds to download all the 6320430 decimal digits.

Jalli · Post by **Jalli** » 15 Dec 2003, 17:10

I never said it couldn't, I said it wouldn't. but hey, as you wan't. Go solve it then...