GRE数学精选试题练习
<p> 1、<span word="To">To</span> <span word="find">find</span> <span word="the">the</span> <span word="median">median</span> <span word="of">of</span> <span word="data">data</span> <span word="given">given</span> <span word="by">by</span> <span word="percentage">percentage</span>给了不同年龄<span word="range">range</span>, 和各个<span word="range">range</span>的<span word="percentage">percentage</span>, 问<span word="median">median</span> 落在哪个<span word="range">range</span>里. 把<span word="percentage">percentage</span>加到50%就是<span word="median">median</span>的<span word="range">range</span>了.担小心一点，<span word="range">range</span>首先要保证是有序排列.</p><p> <span word="Example">Example</span> <span word="for">for</span> <span word="this">this</span>:</p><p> <span word="Given">Given</span>: 10～20 = 20%, 30～50 = 30%, 0～10 = 40%, 20～30 = 10%, 问<span word="median">median</span>在哪个<span word="range">range</span>里.</p><p> 分析： 千万不要上来就加，要先排序，切记!重新排序为： 0～10 = 40%, 10～20 = 20%, 20～30 = 10%, 30～50 = 40%. 然后从小开始加， <span word="median">median</span>落在 10～20这个<span word="range">range</span>里.</p><p> 如果觉得比较玄乎，我的方法，<span word="GRE">GRE</span>大部分的题都可以这么搞。0～10岁 40匹<span word="ETS">ETS</span>猪，10～20岁 20匹<span word="ETS">ETS</span>猪，20～30岁匹<span word="ETS">ETS</span>猪，30～50岁 匹<span word="ETS">ETS</span>猪，这100匹<span word="ETS">ETS</span>猪按着年龄排下来，你说第五十匹<span word="ETS">ETS</span>猪的年龄落在那个范围。</p><p> 2、比较,当<span word="n">n</span>1时，<span word="n">n</span>，1，2 和1，2,3的标准方差谁大<span word="standard">standard</span> <span word="error">error</span> 和 <span word="standard">standard</span> <span word="variation">variation</span> 都是用来衡量一组数据的离散程度的统计数值,只不过由于<span word="standard">standard</span> <span word="error">error</span>中涉及绝对值,在数学上是很难处里的所以,都用标准方差,实际上<span word="standard">standard</span> <span word="error">error</span>更合理一些,它代表了数据和平均值的平均距离.很明显题目中如果<span word="n">n</span>=0的话,0,1,2的离散程度应该和1,2,3的离散程度相同.如果 <span word="n">n</span>0,则<span word="n">n</span>,1,2,的离散程度大于后者,而0<span word="Key">Key</span>: <span word="n">n</span>是整数， 前〉=后，2，3，4，5</p>
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