GMAT数学概念之统计篇.

　　在GMAT数学备考中，考生首先需要了解一部分的GMAT数学概念。只有搞清楚GMAT数学概念，才不至于发生因为看错题目而造成的一些不必要的错误，今天澳际小编就统计类数学概念进行总结，希望可以帮到各位。

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　　GMAT数学概念之统计(descriptive statistics)

　　1.平均数(average or arithmetic mean)

　　2.中数(median)

　　To calculate the median of n numbers，first order the numbers from least to greatest;if n is odd，the median is dined as the middle number，while if n is even，the median is dined as the average of the two middle numbers. For the data 6, 4, 7, 10, 4, the numbers, in order, are 4, 4, 6, 7, 10, and the median is 6, the middle number. For the numbers 4, 6, 6, 8, 9, 12, the median is (6+8 )/2 = 7. Note that the mean of these numbers is 7.5.

　　3.众数(mode)：一组数中的众数是指出现频率最高的数。

　　例：the mode of 7，9，6，7，2，1 is 7。

　　4.值域(range)：表明数的分布的量，其被定义为最大值减最小值的差。

　　例：the range of–1，7，27，27，36 is 36-(-1)= 37。

　　5.标准方差(standard deviation)：

　　One of the most common measures of dispersion is the standard deviation. Generally speaking, the greater the data are spread away from the mean, the greater the standard deviation. The standard deviation of n numbers can be calculated as follows:

　　(1)find the arithmetic mean ;

　　(2)find the differences between the mean and each of the n numbers ;

　　(3)square each of the differences ;

　　(4)find the average of the squared differences ;

　　(5)take the nonnegative square root of this average.

　　Notice that the standard deviation depends on every data value, although it depends most on values that are farthest from the mean. This is why a distribution with data grouped closely around the mean will have a smaller standard deviation than data spread far from the mean.

　　如果考生将GMAT数学概念加以归类，思路会更清晰。考生可以根据归类的GMAT数学概念加以复习。对于GMAT数学概念切莫死记硬背，在理解的基础进行记忆一方面是比较方便记忆，一方面还能真正理解单词的含义，提高准确性。