5. Elvira takes a triplet of numbers and transforms it according to the rule: at each step, each number is replaced by the sum of the other two. What is the difference between the largest and the smallest numbers in the triplet after 2019 applications of this rule, if the initial triplet was $\{100 ; 89 ; 60\}$? If the question allows multiple answers, write them without spaces in ascending order.
Solution. Let's denote the 3 numbers as $\{x ; x+a ; x+b\}$, where $0<a<b$. Then the difference between the largest and the smallest number at any step, starting from the zeroth step, will be an invariant, that is, unchanged and equal to $b$.

$b=100-60=40$.

Answer: 40.