Answer
$|x-600|\leq50$
Work Step by Step
If $a\leq x\leq b$, we can turn this into an absolute value inequality in the following way:
Take the mean of $a$ and $b$: $\frac{a+b}{2}$. This will be equidistant from $a$ and $b$. Thus if we take x's difference from this, it must be within $|a-\frac{a+b}{2}|=|b-\frac{a+b}{2}|$. Thus the inequality will be: $|x-\frac{a+b}{2}|\leq|a-\frac{a+b}{2}|$.
Hence here the inequality is: $|x-\frac{550+650}{2}|\leq|550-\frac{550+650}{2}|\\|x-600|\leq50$
