Proving the Subset Sum Divisible by n

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Discussion Overview

The discussion revolves around proving that for every set of n numbers, there exists a subset whose sum is divisible by n. The scope includes theoretical exploration and mathematical reasoning related to subsets and their properties.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant expresses interest in proving the result and finds it enjoyable.
  • Another participant questions whether the numbers must be in sequence or if any set can be used.
  • A participant asks if a subset can consist of a single number or if it must be a summable subset.
  • Clarification is provided that both the set and subset can be any non-empty set, and that numbers can repeat, using {1,1,2,2,4} as an example.
  • Some participants challenge the definition of a "set," arguing that {1,1,2,2,4} should not be considered a set of 5 numbers, as it simplifies to {1, 2, 4} which is a set of 3 numbers.
  • A later reply suggests that the result applies to sets but can also extend to multisets.
  • One participant proposes a method involving modular arithmetic, stating that if the sums of the first k numbers yield n different results mod n, one must be congruent to n, or if two sums are the same mod n, their difference is congruent to zero mod n.

Areas of Agreement / Disagreement

Participants express differing views on the definition of a "set" and whether the result applies strictly to sets or can include multisets. The discussion remains unresolved regarding the implications of these definitions on the proof.

Contextual Notes

There are limitations regarding the definitions of sets and multisets, as well as the conditions under which the subset sum property holds. The discussion does not resolve these definitions or their implications.

daniel_i_l
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Prove that for every set of n numbers has a subset whose sum is divisible by n. I found this result very interesting. It's also fun to prove!
 
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Must these numbers be in sequence? Like {4,5,6,7,8}, or could it be any set like {1,10}?

EDIT: Never mind...that was a silly question.
 
can this subset be 1 number? or does it have to be summable?
 
Both the set and subset can be any not emty set. But I forgot to mention that numbers can repeat themselves so that in this case {1,1,2,2,4} is a "set" of 5 numbers and to answer ices's question, {1} is a subset of it.
 
No, that is NOT a "set" of 5 numbers! {1,1,2, 2,4}= {1, 2, 4} is a set of 3 numbers!
If you mean something else do not use the word "set".
 
HallsofIvy said:
No, that is NOT a "set" of 5 numbers! {1,1,2, 2,4}= {1, 2, 4} is a set of 3 numbers!
If you mean something else do not use the word "set".

The result holds for sets. daniel_i_l's point was surely that the result naturally extends to multisets.
 
work mod n. given n numbers, (integers), if we sum the first k of them, for k = 1,...,n, and we get n different numbers mod n, then one of them is congruent to n. done.if on the other hand two different sums have the same sum mod n , then subtracting them, gives a sum congr'uent to zero mod n. done again.
 

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