【数学】GMAT数学考试基本概念之统计

　　GMAT数学备考之描述统计(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 defined as the middle number，while if n is even，the median is defined 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*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*大值减*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.

　　GMAT数学基本概念，如果考生加以归类，会感觉没有想象中那么复杂和混乱。考生可以根据归类的GMAT数学基本概念，加以复习和记忆。还要提醒考生的是，GMAT数学的基本概念，*忌讳的是死记硬背，考生*好采用理解式记忆法，GMAT数学基本概念就能轻松搞定。

　　通过上面朗阁对GMAT数学考试基本概念中的统计概念的介绍，相信对于很多计划参加GMAT考试的人来说，可以参考上述的信息来做好GMAT数学考试的备考和准备工作。