GMAT数学之例题解析
<p> 一个包中装有7个红色的物体，5个绿色的物体，问：从中随意取出3个是全红的概率? 【答案】7/44 【思路】 <span word="C">C</span>7,3/<span word="C">C</span>12,3=7/44 (<span word="C">C</span>7,3表示从7个物体中随意取出3个组合数) 4(<span word="X">X</span>-1)(<span word="X">X</span>-1)16，问<span word="X">X</span>是整数的数目? 【答案】2 【思路】 4(<span word="x">x</span>-1)216 2 │<span word="x">x</span>-1│4 <span word="x">x</span>-1,或<span word="x">x</span>3, 且-3 在这些区间的整数是-2，4。所以答案是2个整数。 <span word="An">An</span>=<span word="A">A</span>(<span word="n">n</span>-1)+2<span word="A">A</span>(<span word="n">n</span>-2)，<span word="A">A</span>1=<span word="A">A</span>2=1，2 【答案】43 【思路】 <span word="A">A</span>3=<span word="A">A</span>2+2<span word="A">A</span>1=3 同理按顺序可以推出 <span word="A">A</span>4=5,<span word="A">A</span>5=11,<span word="A">A</span>6=21,<span word="A">A</span>7=43 一个人一年的<span word="income">income</span>当中一部分花掉，另一部分存起来，利率是<span word="r">r</span>。第二年存起来的部分每1 <span word="dollar">dollar</span>变成(1+<span word="r">r</span>)<span word="dollar">dollar</span>。第二年没有收入，将第一年存的钱用来花销，问如果第二年可供花销的钱是第一年花掉的钱的1/2，那么第一年存的钱是收入的几分之几? 【答案】1/(2<span word="r">r</span>+3) 【思路】 设第一年存的钱为<span word="x">x</span>,第一年花的钱<span word="y">y</span> 则有： (1+<span word="r">r</span>)<span word="x">x</span>/<span word="y">y</span>=1/2,所以<span word="y">y</span>=2<span word="x">x</span>(1+<span word="r">r</span>)， 设第一年收入<span word="z">z</span>,则<span word="z">z</span>=<span word="x">x</span>+<span word="y">y</span> 所以 <span word="x">x</span>/<span word="z">z</span>=1/(2<span word="r">r</span>+3) <span word="k">k</span>和<span word="p">p</span>是<span word="positive">positive</span> <span word="constants">constants</span>, 问：以下那个方程一定有一个负数解。 <span word="I">I</span>. <span word="X">X</span>^2+<span word="kX">kX</span>+<span word="p">p</span>=0; <span word="II">II</span>. <span word="X">X</span>^2-<span word="kX">kX</span>+<span word="p">p</span>=0; <span word="III">III</span>. <span word="X">X</span>2+<span word="kX">kX</span>-<span word="p">p</span>=0; <span word="A">A</span>. <span word="I">I</span> <span word="B">B</span>. <span word="II">II</span> <span word="C">C</span>. <span word="III">III</span> <span word="D">D</span>. <span word="II">II</span> <span word="and">and</span> <span word="III">III</span> <span word="E">E</span>. <span word="I">I</span> <span word="and">and</span> <span word="II">II</span> <span word="and">and</span> <span word="III">III</span> 【答案】<span word="C">C</span> 【思路】 运用二次方程根的一般解法： <span word="x">x</span>=-<span word="b">b</span>[<span word="U">U</span>]+<span word="b">b</span>^2-4<span word="ac">ac</span> 开根号/2<span word="a">a</span> 以及<span word="k">k</span>,<span word="p">p</span>是正整数的条件可以很快解得只有3肯定是负解。 以上就是<span word="GMAT">GMAT</span>数学例题及其讲解过程，就如前文所述，解题的关键在于解题思路。正确的解题思路可以让解题变得非常简单，但往往考生在自己答题的过程中会钻入死胡同，而这往往就是一种思维习惯。希望各位考生在备考阶段多种总结，最终都考出好成绩。</p>
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