A pencil is one dollar, and a pencil box is two dollars more expensive than a pencil. Jimmy has seven dollars and bought a pencil box. How many pencils can Jimmy buy？(adapted from $$2009$$ Math kangaroo Problems, Level $$1-2$$, Question \#$$6$$) 
Overseas Competition->Knowledge Point->Word Problem Modules->Applying Addition and Subtraction->Simple Addition and Subtraction
A pencil box costs two dollars more than a pencil, so it\textquotesingle s $1+2=3$ dollars. $7-3=4$. So~He can buy $4\div1=4$~pencils. 