10. There is a four-digit number. By rearranging the digits (none of which are 0) of this four-digit number, the largest new number obtained is 5562 greater than the original number, and the smallest new number is 2700 less than the original number. What is the original four-digit number?
Problem 391
Official solution
\begin{tabular}{|c|}
\hline 10 \\
\hline 4179 \\
\hline
\end{tabular}