How many multiples of $11$ of four digits, of the form $\overline{abcd}$, satisfy that $a\neq b, b\neq c$ and $c\neq a$?
Source: 2016 Peru Cono Sur TST P1
Tags: number theory
How many multiples of $11$ of four digits, of the form $\overline{abcd}$, satisfy that $a\neq b, b\neq c$ and $c\neq a$?