单选题 A study was conducted to determine whether the standard deviation of monthly maintenance cost of an airplane is $500. A sample of 25 airplanes of same model had a mean monthly maintenance cost of $4300 and a standard deviation of $545. Using a 10% level of significance, which of the following is the most appropriate conclusion regarding the difference between the hypothesized value of the population variance and the sample variance?

A、 The population and sample variances are significantly different.
B、 The population and sample variances are not significantly different.
C、 There are no tests that may be used to test variance differences in small samples.

【正确答案】 B

【答案解析】[解析] 由题干可知，本题适用双边检验(χ ² -检验)，检验的基本结构为：

α/2=0.05，df=25-1=24。
检验统计量

基于10%的显著水平和自由度df等于24，经查表可知本题的下限关键值为13.848，上限关键值为36.415。如图所示，因为13.848＜28.514＜36.415，所以原假设成立，即在10%的显著水平下，总体方差和样本方差并无明显差异。