[Archive!] Pure mathematics, physics, chemistry, etc.: brain-training problems not related to trade in any way - page 8

 
AlexEro писал(а) >>

Yes, that's law, not mathematics.

The problem must be understood so that the solution is not trivial. Otherwise it's really jurisprudence ;)

 
Avals >>:

задачу надо понимать так, чтобы решение не было тривиальным. Иначе это действительно юриспруденция ;)

Before I wrote "7th grade" I googled the problem (after presenting my verdict, fair enough) - I did not find the solution, but the problem is one of the Olympiads for the 7th grade. What it means, I do not know.

 

Integer, reciprocity is explicitly stated in the comment on the problem. We are not talking about the reality in which A can say he is friends with B and B will say A is not his friend. And I asked not to google :(

OK, let's replace friendship with something else mutual, but not transitive - say, the attitude "A met B at Aunt Masha's disco club". (By the way, the relation "A lives in the same yard as B" is mutual but, alas, transitive: if A~B and B~C, then A~C.)

AlexEro, in this formulation does the problem suit you?

 

Will someone answer my question or not. How many options with 5 students? You can't count with 5,

but you want to count with 25 :)

 
Richie писал(а) >>

Will someone answer my question or not. How many options with 5 students? You can't count with 5,

but you want to count with 25 :)

0,1,2,3,2 и 1,2,3,4,2

on page 6 wrote.

 

Probably two or three.

Yeah, Avals wrote that. But I'm really interested in finding a general algorithm for the solution, rather than having to deal with each case separately.

 
one of the options :D

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
1 x 25
2
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24 25
3

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23 24 25
4


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22 23 24 25
5



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21 22 23 24 25
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x












20 21 22 23 24 25
7





x










19 20 21 22 23 24 25
8






x








18 19 20 21 22 23 24 25
9







x






17 18 19 20 21 22 23 24 25
10








x




16 17 18 19 20 21 22 23 24 25
11









x


15 16 17 18 19 20 21 22 23 24 25
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x
14 15 16 17 18 19 20 21 22 23 24 25
13











x 14 15 16 17 18 19 20 21 22 23 24 25
14










12 13 x 15 16 17 18 19 20 21 22 23 24 25
15









11 12 13 14 x 16 17 18 19 20 21 22 23 24 25
16








10 11 12 13 14 15 x 17 18 19 20 21 22 23 24 25
17







9 10 11 12 13 14 15 16 x 18 19 20 21 22 23 24 25
18






8 9 10 11 12 13 14 15 16 17 x 19 20 21 22 23 24 25
19





7 8 9 10 11 12 13 14 15 16 17 18 x 20 21 22 23 24 25
20




6 7 8 9 10 11 12 13 14 15 16 17 18 19 x 21 22 23 24 25
21



5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 x 22 23 24 25
22


4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 x 23 24 25
23

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 x 24 25
24
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 x 25
25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 x

Petya needs a different number of friends, so there are 13 in this case)

 

BU_GA_GA!!!

That "solution" assumes its existence from the start. And this is not always the case. This is literally the ONLY thing the Mathematician himself has shown in another thread about limits.

 
Mathemat писал(а) >>

Probably two or three.

Right, Avals wrote it.

How do you imagine it?

Reason: