GMAT數(shù)學(xué)統(tǒng)計(jì)篇概念.

　　在GMAT數(shù)學(xué)備考中，考生首先需要了解一部分的GMAT數(shù)學(xué)概念。只有搞清楚GMAT數(shù)學(xué)概念，才不至于發(fā)生因?yàn)榭村e(cuò)題目而造成的一些不必要的錯(cuò)誤，今天小編就統(tǒng)計(jì)類數(shù)學(xué)概念進(jìn)行總結(jié)，希望可以幫到各位。

　　GMAT數(shù)學(xué)概念之統(tǒng)計(jì)(descriptive statistics)

　　1.平均數(shù)(average or arithmetic mean)

　　2.中數(shù)(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.眾數(shù)(mode)：一組數(shù)中的眾數(shù)是指出現(xiàn)頻率最高的數(shù)。

　　例：the mode of 7，9，6，7，2，1 is 7。

　　4.值域(range)：表明數(shù)的分布的量，其被定義為最大值減最小值的差。

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

　　5.標(biāo)準(zhǔn)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.

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