$$50$$ students stand in a line facing the teacher, and report the number from left to right one by one: $$1$$, $$2$$, $$3$$, .. etc. After reporting, the teacher asks students who reported multiples of $$4$$ turn backwards. Then let the students whose reported number is a multiple of $$6$$ turn backwards.  How many students are still facing teachers? 
Overseas Competition->Knowledge Point->Number Theory Modules->Factors and Multiples->Common Factors and Common Multiples Overseas Competition->Knowledge Point->Calculation Modules->Whole Numbers->Extracting Common Factors from Whole Numbers