Ali, Barb, and Cal were all born on April $$1$$, in different years.  This coming April $$1$$, if I add all their ages together, I\textquotesingle ll get $$9$$.  On that day, Ali\textquotesingle s age could not be． 
Overseas Competition->Knowledge Point->Counting Modules->Permutations and Combinations->Combinations
Ali, Barb, and Cal \emph{were} all born on April $$1$$, in \emph{different} years.  This coming Apr $$1$$, if I add all their ages, I\textquotesingle ll get $$9$$. Since the youngest possible ages are $$1$$ and $$2$$, the oldest possible age is $$6$$. 