费费数学宝典(连载十三)
<p> 以下为大家连载<span word="GMAT">GMAT</span>数学考试备考宝书，费费数学宝典，希望大家备考顺利，成绩高高，都能申请到理想的美国大学!</p><p> 11、已知整数<span word="K">K</span>前所有整数之和为<span word="K">K</span>/2，问<span word="M">M</span>和<span word="N">N</span>之间，包含<span word="M">M</span>和<span word="N">N</span>，整数的和为多少/2-<span word="m">m</span>/2</p><p> 【思路】</p><p> 题中整数<span word="k">k</span>前所有整数之和应包括<span word="k">k</span>，这样表达有模糊的地方，但要是能一眼看出1-<span word="k">k</span>的和为<span word="k">k</span>/2，那也不成问题。</p><p> 将本题换一种方式来表达可能更容易理解一点：</p><p> 求正整数<span word="m">m</span>和正整数<span word="n">n</span>之间，包含<span word="m">m</span>和<span word="n">n</span>，整数的和为多少/2，1-<span word="n">n</span>的和为<span word="n">n</span>/2，稍微复杂一点，但不会出现理解上的问题。</p><p> 12、8 <span word="marbles">marbles</span> <span word="in">in</span> <span word="a">a</span> <span word="bag">bag</span>, 4 <span word="red">red</span> <span word="and">and</span> 4 <span word="white">white</span>. <span word="Randomly">Randomly</span> <span word="get">get</span> 3 <span word="marbles">marbles</span> <span word="out">out</span> <span word="of">of</span> <span word="the">the</span> <span word="bag">bag</span>, <span word="whats">whats</span> <span word="the">the</span> <span word="probability">probability</span> <span word="that">that</span> <span word="at">at</span> <span word="least">least</span> 1 <span word="of">of</span> <span word="the">the</span> 3 <span word="marbles">marbles</span> <span word="is">is</span> <span word="red">red</span>?</p><p> 【答案】1-<span word="c">c</span>/<span word="c">c</span></p><p> 【思路】剪去没有红色的</p><p> 13、两个三角形相似，面积比为1:2。小三角形一边长为<span word="A">A</span>，大三角形类似的一条边为<span word="B">B</span>，用<span word="A">A</span>来表示<span word="B">B</span>的长度?</p><p> 【答案】根号2<span word="a">a</span> </p><p> </p>
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