[Archive!] Pure mathematics, physics, chemistry, etc.: brain-training problems not related to trade in any way - page 4
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Graphically the problem is solved quite simply. But how to solve this combinatorics mathematically??? I can't figure it out....
Although I decided that Petya is not one of 25 classmates with different number of friends, and his number of friends may be the same as someone else's..... But there is no other way, so my version is 12 if only from the point of view of drawing. Or 13?) Confused in columns...
Figaro, ты можешь показать графическое решение?
2 Farnsworth: но ведь ответ-то - 12 или 13.
Bullshit is about 12 or 13. If you put Vasya instead of Petya in the condition, then Vasya won't have 12 or 13, but something else. And how does the problem tell them apart? It doesn't.
is it the riddle of Ocean and his 13 friends? :)
Mathematically, I don't know. It's in the realm of combinatorics.
Graphically, it's something like this.
AlexEro, I have already given evidence that Petya cannot be "0", "1" or "25". But the problem has not yet been solved.
Брехня - насчёт 12 или 13. Если в условии поставить не Петя, а Вася, то у Васи будет не 12 или 13, а как-то по другому. А как их различает задача? А никак.
It does, and very much so. This is the view from Petya's side. From the side of almost everyone else it is different.
Figaro, can you show the graphical solution?
Draw 5 points of classmates, and a point in the distance - Petya, take a pencil and connect the points, counting the number of connections and considering the condition of the problem. (At first I try to do without Petya and when I "sink", I add missing connections with him.) For a larger number of points I will keep the "similarity". There's really a problem with the odds and evens. Shit. Right, 13 coming out.
And by the way...
The condition: "...all of his 25 classmates have a different number of friends...".
It means that only these 25 have different number of friends.
In other words, Petya's number of friends can be the same as the number of friends of one of his classmates.
Брехня - насчёт 12 или 13. Если в условии поставить не Петя, а Вася, то у Васи будет не 12 или 13, а как-то по другому. А как их различает задача? А никак.
where I wrote that "2 Farnsworth: but the answer is 12 or 13." Where did you find that, where did you look? I gave my answer (25-2) or (25-3) (not sure)
I realise that we have to look at symmetrical matrices of people's relationships somehow. But we have agreed not to go beyond elementary categories.