If the correct time now is $$1:15$$ P.M., and if my clock stopped running three and one-half hours ago, when did it stop running? 
Overseas Competition->Knowledge Point->Counting Modules->Permutations and Combinations->Combinations
One hour ago the time was $$12:15$$ P.M.; two hours ago the time was $$11:15$$ A.M.; three hours ago the time was $$10:15$$ A.M. Three and one-half hours ago the time was $$9:45$$ A.M. 