$$2$$ apples and $$3$$ peaches cost $$$11$$.  $$2$$ apples and $$2$$ peaches cost $$$8$$.  What is the cost of an apple? 
Overseas Competition->Knowledge Point->Word Problem Modules->Equation Word Problems->Equivalent Substitution in Equation Word Problems
$$2$$ apples $$+\textasciitilde3$$ peaches$$\to $$ ＄$$11$$  $$2$$ apples $$+\textasciitilde2$$ peaches $$\to $$ ＄$$8$$  $$1$$ peach $$\to $$ ＄$$3$$  $$2$$ apples $$+$$ ($$2$$ $$\times$$ ＄$$3$$) $$\to $$ ＄$$8$$  $$2$$ apples $$\to $$ ＄$$8\textasciitilde-$$ ＄$$6=$$＄$$2$$  $$1$$ apple $$\to $$ ＄$$2\div2=$$＄$$1$$  The cost of an apple is ＄$$1$$. 