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February 17th, 2003, 02:24 AM
SeventhStar

okay that's what i thought of....
if a+b = s and a*b = p
p is not a product of two prime numbers
therefore s cannot be a sum of two prime numbers otrewise S wouldn't have known for sure that P cannot know the numbers that means that 3+6=9 could not be it becaouse 9 can be 2+7
so s is one of these numbers and both men nknow it after the second statement 11, 17... etc nubers that cannot be made like a sum of two prime numbers

so suppose S knew 11 and P knew 24 p whould've guessed the numbers after S saying that he knew P wouldn't. but s would be wondering between 2*9 = 18, 3*8 =24 and 5*6 = 15 so the sum cannot be eleven
February 17th, 2003, 02:44 AM
SeventhStar

so s is not 17 becaouse p could be 52=3*14 or 66 = 11*6 and S won't know the answer again
February 17th, 2003, 02:51 AM
SeventhStar

so a is prime and b is ot the type 2*m where m is a prime number and s can has only one way of bein represented like a sum of this kind of numbers so s is not 11 and not 17 and not 23
February 17th, 2003, 02:54 AM
SeventhStar

so a is 13 and b is 22
February 17th, 2003, 03:32 AM
Simon666

Quote:

Originally posted by SeventhStar
therefore s cannot be a sum of two prime numbers...

So you're saying s can only be odd numbers (as each even number can be written as the sum of two primes) minus all odd numbers that are equal to a prime number + 2. And we already know that p cannot be the product of two prime numbers.

That already excludes quite some possibilities.
February 17th, 2003, 03:51 AM
SeventhStar

Quote:

Originally posted by Simon666
each even number can be written as the sum of two primes

taht's still not proven but it's true for all numbers less than 100 000
February 17th, 2003, 04:07 AM
Simon666

Quote:

Originally posted by SeventhStar
taht's still not proven but it's true for all numbers less than 100 000

I think it is calculated just a little bit further than 100.000, according to GStercken 4*10^14. So I doubt it would not be true. :D:D:D
February 17th, 2003, 04:13 AM
SeventhStar

Quote:

Originally posted by Simon666

I think it is calculated just a little bit further than 100.000, according to GStercken 4*10^14. So I doubt it would not be true. :D:D:D

okay but it isn't proven for sure.
February 17th, 2003, 04:15 AM
Simon666

Quote:

Originally posted by SeventhStar
okay but it isn't proven for sure.

Look, if it is proven for at least all numbers between 2 and 99 that is already enough for this riddle. :rolleyes:
February 17th, 2003, 04:22 AM
SeventhStar

Quote:

Originally posted by Simon666

Look, if it is proven for at least all numbers between 2 and 99 that is already enough for this riddle. :rolleyes:

Yep! And I think that:

Quote:

]Originally posted by me
A is 13 and B is 22
February 17th, 2003, 04:24 AM
Simon666

I saw on a website once it is 4 and 47, but didn't find an explanation and it might just have been a guess.
February 17th, 2003, 04:37 AM
SeventhStar

maybe there can be more than one answers...
February 17th, 2003, 04:51 AM
Simon666

Quote:

Originally posted by SeventhStar
maybe there can be more than one answers...

Maybe there is no answer at all. :D:D:D
February 17th, 2003, 04:58 AM
SeventhStar

Well we wait for Elrond to say
February 17th, 2003, 05:09 AM
SeventhStar

just checked my calcualations :rolleyes:
13 and 22 is not it
but I like 47 and 4
I'll check it out
February 18th, 2003, 01:48 AM
SeventhStar

4 and 47 can also not be it.
I give up! So Elrod please post the answer!
and let's proceed
February 18th, 2003, 08:30 AM
Elrond

Sorry, I've been (and still am) quite busy.

The answer I had was 3 and 14 (S:17, P:52).

Basically, when you calculate all the possibilites of products for each sum that has not two primary numbers you'll have a list like:

S:11 -> P: 18 24 28 30
S:17 -> P: ...

Then you remove all products that appear in multiple lines, because they would have prevented P to know for sure the possible result. Finally the only line with one product for a sum is:
S:17 -> P:52.

I don't have time to give additional explanation. If ou are not happy with that, just don't count the question or remove one point to me for a flawed or badly explained question. Then continue with additional questions.
February 18th, 2003, 08:39 AM
SeventhStar

I don't like this

4 and 13
6 and 11
8 and 19

are just as good for me
February 18th, 2003, 02:22 PM
SolarFlare

I think that question totally killed this thread
February 18th, 2003, 02:37 PM
galathaea

3 * 14 = 42
February 23rd, 2003, 05:30 AM
SeventhStar

Quote:

Originally posted by solarflare
I think that question totally killed this thread

so lets try to keep it alive then ;)

sooooo

two men were walking through a desert. They reached a river that crossed the desert. Both of them couldn't swim and the river was too big to be crossed without a boat. But there was a boat. It could only carry ONE man. The two used it to cross the river and went their ways dry. How was this possible.
February 23rd, 2003, 09:59 AM
gstercken

Did they use a rope?

Assuming there really were rivers in deserts?
February 23rd, 2003, 11:23 AM
SolarFlare

Quote:

Originally posted by SeventhStar
two men were walking through a desert. They reached a river that crossed the desert. Both of them couldn't swim and the river was too big to be crossed without a boat. But there was a boat. It could only carry ONE man. The two used it to cross the river and went their ways dry. How was this possible.

It's obvious: the big man ate the small man and crossed the river, then regurgitated the small man.
February 24th, 2003, 02:32 AM
SeventhStar

Quote:

Originally posted by gstercken
Did they use a rope?

Assuming there really were rivers in deserts?

noooo no rope
February 24th, 2003, 02:33 AM
SeventhStar

Quote:

Originally posted by solarflare

It's obvious: the big man ate the small man and crossed the river, then regurgitated the small man.

noo no canibalism
February 24th, 2003, 02:53 AM
Elrond

The man are not together! Each man is on a different side of the river. It means one takes the boat to cross one way, and the second use the boat on the other way.
February 24th, 2003, 03:02 AM
SeventhStar

Quote:

Originally posted by Elrond
The man are not together! Each man is on a different side of the river. It means one takes the boat to cross one way, and the second use the boat on the other way.

yes that's right ;)
February 24th, 2003, 04:57 PM
SolarFlare

Quote:

Originally posted by SeventhStar
The two used it to cross the river and went their ways dry.

A lesser man than Elrond would not have noticed this. Wait a minute, I didn't notice this! :eek:
February 24th, 2003, 06:44 PM
morrowasted

hey you guys i have a question:
why does everyone discriminate against 14 year old programmers????
February 24th, 2003, 07:59 PM
SolarFlare

Quote:

Originally posted by morrowasted
why does everyone discriminate against 14 year old programmers????

How so?
February 24th, 2003, 08:30 PM
Mick

Quote:

Originally posted by morrowasted
hey you guys i have a question:
why does everyone discriminate against 14 year old programmers????

Yep I cared so much to check your age...NoT....it's in your head...it's all in my head ;)
February 24th, 2003, 09:58 PM
morrowasted

HEY! see what i mean? j/k.
well I look at people's profiles!
February 24th, 2003, 10:00 PM
morrowasted

hey solarflare, why the C++ looking code in your sig? OH YEAH! Codeguru forums... i forget when i am in the chitchat section
February 24th, 2003, 10:05 PM
SolarFlare

Quote:

Originally posted by morrowasted
HEY! see what i mean? j/k.
well I look at people's profiles!

Okay, let's take a look at my signature, if that's what you mean:
"Those who cling to life die and those who defy death live. -Sun Tzu"
I don't get it, is that somehow discriminatory against you?
February 24th, 2003, 10:10 PM
morrowasted

huh? no i meant the:

cout << endl;
return 0;
}

i forgot we were using codeguru forums. i am just messin around about discrimination, im not serious.
Lesson One:
NEVER listen to me, unless its about VB6 or women
February 25th, 2003, 03:09 AM
Simon666

Quote:

Originally posted by morrowasted
i forgot we were using codeguru forums. i am just messin around about discrimination, im not serious.
Lesson One:
NEVER listen to me, unless its about VB6 or women

I don't take you serious already: didn't you mean especially instead of unless? :D
February 25th, 2003, 03:24 PM
SolarFlare

Quote:

Originally posted by Simon666
I don't take you serious already: didn't you mean especially instead of unless? :D

Let's not even go there... if I looked for all the things you've said that could be reversed, then...

(I'd be wasting my time)
February 26th, 2003, 02:37 AM
SeventhStar

ok - a mathematical one:

There's a railroad that goes near two towns. Both towns need to have a railstation but the state doesn't have enough money for it. So they decide to buld one railstation betwween the two towns but so that the sum of the distances between each town and the stations is minimal. So you have the picture with written distances. Where on the railroad should me made point C so AC+BC is minimal.
February 26th, 2003, 02:38 AM
SeventhStar

1 Attachment(s)

ooops!!!
Forgot the attachment
February 26th, 2003, 03:20 PM
SolarFlare

Quote:

Originally posted by SeventhStar
There's a railroad that goes near two towns. Both towns need to have a railstation but the state doesn't have enough money for it. So they decide to buld one railstation betwween the two towns but so that the sum of the distances between each town and the stations is minimal. So you have the picture with written distances. Where on the railroad should me made point C so AC+BC is minimal.

nx/(x+y) miles East of the Western intersection.

[edit: my original answer was nx/(x+y) units, but I looked at the map again and saw the 'miles' labels.]
February 26th, 2003, 04:15 PM
galathaea

Its a simple reflection problem.... since the shortest distance between two points is a line, just reflect one of the cities through the railroad line and connect the two cities by a line. The point where the line intersects the railroad line is where you put it...
February 26th, 2003, 06:05 PM
galathaea

By the way, I wasn't suggesting solarflare's answer was incorrect. I was just showing how you solve it, since the brute force method would be a differentiation problem and there is a nice, elegant solution to problems like these using simple ratios.

(I never get here in time to actually answer a problem -- except for that one -- so I wanted to contribute, however minor :) )
February 26th, 2003, 06:26 PM
SolarFlare

Quote:

Originally posted by galathaea
the brute force method would be a differentiation problem and there is a nice, elegant solution to problems like these using simple ratios.

When I look at a problem like that, the first thing I do is figure out what methods I could use to solve it completely. Of course when I saw minimize I thought differentiation, but it turned out that it would have been horrifically ugly as galathaea pointed out. So I stuck with x/? = y/n-?, and solved for ?.
February 28th, 2003, 02:19 AM
SeventhStar

soo can any one ask a good question now???
February 28th, 2003, 03:16 AM
Simon666

Quote:

Originally posted by SeventhStar
soo can any one ask a good question now???

That's a good question. Keep going. :D:p:p
February 28th, 2003, 06:43 AM
Wfranc

Quote:

Originally posted by SeventhStar
soo can any one ask a good question now???

Questions not related to maths or physics are also Okay ? I mean funny stuff ? :D :D
February 28th, 2003, 07:26 AM
SolarFlare

Quote:

Originally posted by Wfranc
Questions not related to maths or physics are also Okay ? I mean funny stuff ? :D :D

Okay, if a clown has five apples, and I take away two apples...
February 28th, 2003, 09:42 AM
Wfranc

Quote:

Okay, if a clown has five apples, and I take away two apples...

Alright, if You can answer the questions I make, this means You are so much superior to others:) and of course, You could take even 5 apples:D.
I am trying to think about the funiest question for You Ms/Mr Solarflare:D. And remember to try your best to give out the correct answer to be in the first rank Okay ?
February 28th, 2003, 09:45 AM
Simon666

Quote:

Originally posted by Wfranc
Okay ?

Yes.

That is one question I was able to answer. Yippie, I'm superior to others. :D :p
February 28th, 2003, 10:24 AM
Wfranc

Quote:

Originally posted by Simon666

Yes.

That is one question I was able to answer. Yippie, I'm superior to others. :D :p

Oh Gosh, you have forgoten what happened, Simon :) :p, I like it much,....really. ;)

I will post a question later. :) :D

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