Mr. $$A$$ owns a home worth ＄$$10000$$. He sells it to Mr. $$B$$ at a $$10\textbackslash\%$$ profit based on the worth of the house. Mr. $$B$$ sells the house back to Mr. $$A$$ at a $$10\textbackslash\%$$ loss. Then: ($$1951$$ AHSME Problem, Question \#$$5$$) 
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Mr. $$ A$$ sells his home for $$(1 + 10\textbackslash\%)\times 10000$$ dollars$$= 1.1\times 10000$$ dollars$$ = 11000$$ dollars to Mr. $$ B$$. Then, Mr. $$ B$$ sells it at a price of $$(1- 10\textbackslash\%)\times 11000$$ dollars $$= 0.9\times 11000$$ dollars $$= 9900$$ dollars, thus $$11000- 9900=\boxed{ (\rm B) \textasciitilde A\textasciitilde makes\textasciitilde1100\textasciitilde on\textasciitilde the\textasciitilde deal}$$. 