MathDB
A Large Table

Source: 1997 National High School Mathematics League, Exam Two, Problem 3

March 6, 2020
geometryrectangle

Problem Statement

In a 100×25100\times25 rectangle table, fill in a positive real number in each blank. Let the number in the iith line, the jjth column be xi,j(i=1,2,,100,j=1,2,,25)x_{i,j}(i=1,2,\cdots,100,j=1,2,\cdots,25) (shown in Fig.1 ). Then, we rearrange the numbers in each column: x1,jx2,jx100,j(j=1,2,,25)x'_{1,j}\geq x'_{2,j}\geq\cdots\geq x'_{100,j}(j=1,2,\cdots,25) (shown in Fig.2 ). Find the minumum value of kk, satisfying: As long as j=125xi,j1\sum_{j=1}^{25}x_{i,j}\leq1 for numbers in Fig.1 (i=1,2,,100i=1,2,\cdots,100), then j=125xi,j1\sum_{j=1}^{25}x'_{i,j}\leq1 for iki\geq k in Fig.2. Fig.1\\ \begin{tabular}{|c|c|c|c|} \hline $x_{1,1}$&$x_{1,2}$&$\cdots$&$x_{1,25}$\\ \hline $x_{2,1}$&$x_{2,2}$&$\cdots$&$x_{2,25}$\\ \hline $\cdots$&$\cdots$&$\cdots$&$\cdots$\\ \hline $x_{100,1}$&$x_{100,2}$&$\cdots$&$x_{100,25}$\\ \hline \end{tabular} \qquadFig.2\\ \begin{tabular}{|c|c|c|c|} \hline $x'_{1,1}$&$x'_{1,2}$&$\cdots$&$x'_{1,25}$\\ \hline $x'_{2,1}$&$x'_{2,2}$&$\cdots$&$x'_{2,25}$\\ \hline $\cdots$&$\cdots$&$\cdots$&$\cdots$\\ \hline $x'_{100,1}$&$x'_{100,2}$&$\cdots$&$x'_{100,25}$\\ \hline \end{tabular}