Arjun gets his hair cut every $$2$$ weeks.  Yahya gets his hair cut every $$10$$ days.  They both got their hair cut on the same day. How long until this happens again? 
Overseas Competition->Knowledge Point->Number Theory Modules->Factors and Multiples->Common Factors and Common Multiples->Common Multiples and Least Common Multiples->Least Common Multiple of Two Numbers