Source: OLCOMA Costa Rica National Olympiad, Final Round, 2016 Shortlist N1 day1
Tags: algebra, floor function
Find all $x \in R$ such that $$ x - \left[ \frac{x}{2016} \right]= 2016$$, where $[k]$ represents the largest smallest integer or equal to $k$.
So $x=\left[\frac{x}{2016} \right]+2016$
$\implies x \ge \frac{x}{2016}+2016$
$\implies x \ge 2016 \times \frac{2016}{2015}$
Also $x < 2017 \times \frac{2016}{2015}$
$\implies 2016 \times \frac{2016}{2015} \le x < 2017 \times \frac{2016}{2015}$
$\implies 1 < \frac{2016}{2015} \le \frac{x}{2016} < \frac{2017}{2015} < 2$
$\implies \left[\frac{x}{2016} \right]=1$
Thus $x=1+2016=\boxed{2017}$ is the only solution.
$x=2016a+b$ where $0 \leq b<2016$ and $a$ is integer
$2015a+b=2016$
$0<2015a<2016 \to a=1,b=1,x=2017$