At the school scavenger hunt, class $A$, $B$, $C$ each has $45$, $75$, $210$ students who want to particpate. The participating students will need to split into groups of the same size. They can\textquotesingle t group up with students from other classes. How many students will each group have? 
Overseas Competition->Knowledge Point->Number Theory Modules->Factors and Multiples->Common Factors and Common Multiples->Common Factors and the Greatest Common Factors->The Greatest Common Factor of Multiple Numbers