Difference between revisions of "1988 IMO Problems/Problem 2"

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For which values of <math>n</math> can one assign to every element of <math>B</math> one of the numbers <math>0</math> and <math>1</math> in such a way that <math>A_i</math> has <math>0</math> assigned to exactly <math>n</math> of its elements?
 
For which values of <math>n</math> can one assign to every element of <math>B</math> one of the numbers <math>0</math> and <math>1</math> in such a way that <math>A_i</math> has <math>0</math> assigned to exactly <math>n</math> of its elements?
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== See Also ==
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{{IMO box|year=1988|num-b=1|num-a=3}}

Revision as of 06:22, 28 March 2019

Problem

Let $n$ be a positive integer and let $A_1, A_2, \cdots, A_{2n+1}$ be subsets of a set $B$.

Suppose that

(a) Each $A_i$ has exactly $2n$ elements,

(b) Each $A_i\cap A_j$ $(1\le i<j\le 2n+1)$ contains exactly one element, and

(c) Every element of $B$ belongs to at least two of the $A_i$.

For which values of $n$ can one assign to every element of $B$ one of the numbers $0$ and $1$ in such a way that $A_i$ has $0$ assigned to exactly $n$ of its elements?

See Also

1988 IMO (Problems) • Resources
Preceded by
Problem 1
1 2 3 4 5 6 Followed by
Problem 3
All IMO Problems and Solutions