3. A three-digit number $x y z$ (where $x$, $y$, and $z$ are distinct), rearranging its digits to form the largest and smallest possible three-digit numbers. If the difference between the largest and smallest three-digit numbers is equal to the original three-digit number, then this three-digit number is $\qquad$
3.495.

Let the three-digit number $\overline{y z}$, after rearrangement, form the largest three-digit number $\overline{a b c}(a>b>c)$, then the smallest three-digit number is $\overline{c b a}$.
Since $1 \leqslant a \leqslant 9,1 \leqslant b \leqslant 9,1 \leqslant c \leqslant 9$, and
$$
\begin{array}{l}
\overline{a b c}-\overline{c b a}=(100 a+10 b+c)-(100 c+10 b+a) \\
=99(a-c)
\end{array}
$$

is a multiple of 99, hence the three-digit number $\overline{x y z}$ sought is also a multiple of 99.
The three-digit multiples of 99 are only 8: $198,297,396$, $495,594,693,792,891$.
Upon verification, only 495 meets the requirement.