2008年AMC10竞赛B第18题 2008年AMC12竞赛B第10题
$$2008-AMC12B-10$$  Bricklayer Brenda would take $$9$$ hours to build a chimney alone, and bricklayer Brandon would take $$10$$ hours to build it alone. When they work together they talk a lot, and their combined output is decreased by $$10$$ bricks per hour. Working together, they build the chimney in $$5$$ hours. How many bricks are in the chimney?  瓦工布伦达单独建造一个烟囱需要花费 $9$$ 小时，而瓦工布兰登单独建造它需要花费 $10$$ 小时。 当他们一起工作时，他们会说很多话，他们的总产量每小时减少 10 美元。 他们一起工作，在 $5$$ 小时内建造了烟囱。 烟囱里有多少块砖？
美国AMC10/12->Knowledge Point->Algebra->Application->Equation Word Problems 课内体系->知识点->等式与不等式->等式->方程组的解集
Let $$x$$ be the number of bricks in the chimney, Using $$d=vt$$, we get $$x=\left( \frac{x}{9}+\frac{x}{10}-10 \right)\cdot \left( 5 \right)$$. Solving for $$x$$, we get $$900\Rightarrow \text{B}$$. 