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方差是各个数据与平均数之差的平方的平均数,用来度量随机变量和其数学期望(即均值)之间的偏离程度.在许多实际问题中,研究随机变量和均值之间的偏离程度有着很重要的意义.在高考中关于方差的考查每年都有,主要考查基本概念和计算方法.近来,一道关于分组方差的计算题在各个名校的高考模拟题中出现,原题是:某班40人随机平均分成两组,两组学生一次考试的成绩情况如后,第一组平均分90,标准差为6,第二组平均分为80,标准差为4,则全班成绩的标准差为.笔者研究后将其推广,
Variance is the average of the squares of the differences between the individual data and the average and is used to measure the degree of deviation between the random variable and its mathematical expectation (ie mean). In many practical problems, the degree of deviation between the random variable and the mean Has a very important significance in the college entrance examination on the variance of the test every year, the main test of basic concepts and calculation methods recently, a group of variance calculation questions in the elite college entrance examination simulation questions appear, the original title is: a class 40 were randomly divided into two groups at random, two groups of students after an examination of the results as follows, the first group average 90, standard deviation of 6, the second group average of 80, the standard deviation of 4, the standard class performance Poor for the author after the promotion of its research,