Mary and Jimmy are eating ice cream of the same size. Jimmy eats ice cream twice as fast as Mary. Mary finishes in four minutes. How many minutes Jimmy need?~(adapted from $$2008$$ Math kangaroo Problems, Level $$1-2$$, Question \#$$6$$) 
Overseas Competition->Knowledge Point->Word Problem Modules->Unitary Method Problems->Finding the Total Value using Unitary Method
Jimmy\textquotesingle s speed is twice as fast as Mary\textquotesingle s, and the ice cream they eat is the same size, so Jimmy\textquotesingle s time is only half as long as Mary\textquotesingle s, that is, $4$$\div$$2= $$2$ minutes. 