Ron\textquotesingle s work day is half over at $$1:15$$ P.M. if he starts work at $$9:30$$ A.M., his work day ends at． 
Overseas Competition->Knowledge Point->Combinatorics->Time Problem->Time Calculation
From $$9:30$$ A.M. until $$1:15$$ P.M. is $$3$$ hours and $$45$$ minutes. Add $$3$$ hours and $$45$$ minutes to $$1:15$$ P.M. to get $$5:00$$ P.M.. 