GMAT数学备考资料：练习+讲解（7）
<p> 下面<span word="GMAT">GMAT</span>思为大家整理了<span word="GMAT">GMAT</span>数学备考资料：练习+讲解（7），供考生们参考，以下是详细内容。</p><p> 1、<span word="In">In</span> <span word="an">an</span> <span word="insurance">insurance</span> <span word="company">company</span>, <span word="each">each</span> <span word="policy">policy</span> <span word="has">has</span> <span word="a">a</span> <span word="paper">paper</span> <span word="record">record</span> <span word="or">or</span> <span word="an">an</span> <span word="electric">electric</span> <span word="record">record</span>, <span word="or">or</span> <span word="both">both</span> <span word="of">of</span> <span word="them">them</span>. 60 <span word="percent">percent</span> <span word="of">of</span> <span word="the">the</span> <span word="policies">policies</span> <span word="having">having</span> <span word="incorrect">incorrect</span> <span word="paper">paper</span> <span word="record">record</span> <span word="have">have</span> <span word="incorrect">incorrect</span> <span word="electric">electric</span> <span word="record">record</span> <span word="and">and</span> 75 <span word="percent">percent</span> <span word="of">of</span> <span word="the">the</span> <span word="policies">policies</span> <span word="having">having</span> <span word="incorrect">incorrect</span> <span word="electric">electric</span> <span word="record">record</span> <span word="have">have</span> <span word="incorrect">incorrect</span> <span word="paper">paper</span> <span word="record">record</span>. 3 <span word="percent">percent</span> <span word="of">of</span> <span word="all">all</span> <span word="the">the</span> <span word="policies">policies</span> <span word="have">have</span> <span word="both">both</span> <span word="incorrect">incorrect</span> <span word="paper">paper</span> <span word="and">and</span> <span word="incorrect">incorrect</span> <span word="electric">electric</span> <span word="records">records</span>. <span word="If">If</span> <span word="we">we</span> <span word="randomly">randomly</span> <span word="pick">pick</span> <span word="out">out</span> <span word="one">one</span> <span word="policy">policy</span>, <span word="what">what</span> <span word="is">is</span> <span word="the">the</span> <span word="probability">probability</span> <span word="that">that</span> <span word="it">it</span> <span word="is">is</span> <span word="one">one</span> <span word="having">having</span> <span word="both">both</span> <span word="correct">correct</span> <span word="paper">paper</span> <span word="and">and</span> <span word="correct">correct</span> <span word="electric">electric</span> <span word="record">record</span>?</p><p> 【答案】94%</p><p> 【思路】</p><p> 设总数为<span word="X">X</span> <span word="policies">policies</span>，则既有非<span word="P">P</span>又有非<span word="E">E</span>为3%<span word="X">X</span>;60%的非<span word="P">P</span>中为非<span word="E">E</span>，则非<span word="P">P</span>为3%<span word="X">X</span>/60%;75%的非<span word="E">E</span>为非<span word="P">P</span>，则非<span word="E">E</span>为3%/75%，那么非<span word="P">P</span>与非<span word="E">E</span>一共有 ，那么<span word="P">P</span>与<span word="E">E</span>一共有<span word="X">X</span>-，则其概率为/<span word="X">X</span>=94%</p><p> 2、<span word="If">If</span> <span word="for">for</span> <span word="all">all</span> <span word="x">x</span>, <span word="x">x</span>^2+<span word="ax">ax</span>+<span word="b">b</span> = ^2, <span word="then">then</span> <span word="a">a</span> =?</p><p> <span word="b">b</span>=0;</p><p> <span word="c">c</span>=-3;</p><p> 【答案】<span word="B">B</span></p><p> 【思路】<span word="x">x</span>^2+<span word="ax">ax</span>+<span word="b">b</span> = ^2= <span word="x">x</span>^2+2<span word="cx">cx</span>+<span word="c">c</span>^2，则<span word="A">A</span>=2<span word="C">C</span>，只要知道<span word="C">C</span>的值就可以知道<span word="A">A</span>值了</p><p> <span word="x">x</span>^2+<span word="ax">ax</span>+<span word="b">b</span> = ^2= <span word="x">x</span>^2+2<span word="cx">cx</span>+<span word="c">c</span>^2</p><p> <span word="x">x</span>^2+<span word="ax">ax</span>+<span word="b">b</span> = <span word="x">x</span>^2+2<span word="cx">cx</span>+<span word="c">c</span>^2</p><p> 化简后：<span word="x">x</span>+=0</p><p> 因为对于所有的<span word="x">x</span>值，上式均成立，则<span word="a">a</span>-2<span word="c">c</span>与<span word="b">b</span>-<span word="c">c</span>^2必须同时为0;</p><p> <span word="a">a</span>-2<span word="c">c</span>=0</p>
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