Question 33
We are given $21$ square tiles of the same size. The number $1$ is written on four tiles; the number $2$ on two tiles; the number $3$ on seven tiles; the number $4$ on $8$ tiles. Using $20$ of these tiles, Dimitar formed a rectangle with dimensions $4$ by $5$. In the formed rectangle the sum of the numbers in every row is the same, and the sum of the numbers in every column is the same. Which number is on the unused tile?