Difference between revisions of "1994 OIM Problems/Problem 5"

(Created page with "== Problem == Let <math>n</math> and <math>r</math> be two positive integers. We wish to construct <math>r</math> subsets <math>A_1, A_2, \cdots , A_r</math> of <math>{0,1,......")
 
 
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Let <math>n</math> and <math>r</math> be two positive integers. We wish to construct <math>r</math> subsets <math>A_1, A_2, \cdots , A_r</math> of <math>{0,1,... ,n-1}</math> each of them with exactly <math>k</math> elements and such that, for each integer <math>x</math>, <math>0 \le x \le n-1</math>, there exist <math>x_1</math> in <math>A_1</math>, <math>x_2</math> in <math>A_2</math>, <math>\cdots</math>, <math>x_r</math> in <math>A_r</math> (one element in each set) with
 
Let <math>n</math> and <math>r</math> be two positive integers. We wish to construct <math>r</math> subsets <math>A_1, A_2, \cdots , A_r</math> of <math>{0,1,... ,n-1}</math> each of them with exactly <math>k</math> elements and such that, for each integer <math>x</math>, <math>0 \le x \le n-1</math>, there exist <math>x_1</math> in <math>A_1</math>, <math>x_2</math> in <math>A_2</math>, <math>\cdots</math>, <math>x_r</math> in <math>A_r</math> (one element in each set) with
  
<cmath>x = x+1+x+2+ \cdots +x_r</cmath>
+
<cmath>x = x_1+x_2+ \cdots +x_r</cmath>
  
 
Find the smallest possible value of <math>k</math> as a function of <math>n</math> and <math>r</math>.
 
Find the smallest possible value of <math>k</math> as a function of <math>n</math> and <math>r</math>.

Latest revision as of 13:32, 13 December 2023

Problem

Let $n$ and $r$ be two positive integers. We wish to construct $r$ subsets $A_1, A_2, \cdots , A_r$ of ${0,1,... ,n-1}$ each of them with exactly $k$ elements and such that, for each integer $x$, $0 \le x \le n-1$, there exist $x_1$ in $A_1$, $x_2$ in $A_2$, $\cdots$, $x_r$ in $A_r$ (one element in each set) with

\[x = x_1+x_2+ \cdots +x_r\]

Find the smallest possible value of $k$ as a function of $n$ and $r$.

~translated into English by Tomas Diaz. ~orders@tomasdiaz.com

Solution

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See also

https://www.oma.org.ar/enunciados/ibe9.htm