parmenides51 wrote: A chessboard $1000 \times 1000$ is covered by dominoes $1 \times 10$ that can be rotated. We don't know which is the cover, but we are looking for it. For this reason, we choose a few $N$ cells of the chessboard, for which we know the position of the dominoes that coever them. Which is the minimum $N$ such that after the choice of $N$ and knowing the dominoed that cover them, we can be sure and for the rest of the cover? (Bulgaria) Can you please elaborate the question, i cannot understand the "cover" part

a domino $1\times 10$ may cover an area $1\times 10=10$ , $2$ dominoes $1x10$ may cover a area of $2\times 1\times 10=20$, $3$ dominoes coveran area of $30$ , and so on but it can be done in many ways, ti depends how you place them in the plane (there might be hole, gaps among them), probably no overlaping of the dominoes may take place, I hope the covering makes sense now