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【OG20-P169-151题】
For each student in a certain class, a teacher adjusted the student’s test score using the formula y = 0.8x + 20, where x is the student’s original test score and y is the student’s adjusted test score. If the standard deviation of the original test scores of the students in the class was 20, what was the standard deviation of the adjusted test scores of the students in the class?
分析A选项
分析B选项
分析C选项
分析D选项
分析E选项
我有更好的解析 
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答案 B
【解析】
序列中每一个数同时加上一个常数，标准差、保持不变！ 序列中每一个数乘以一个常数X，则标准差扩大X倍。 所以，修正后的标准差应该是20×0.8=16。
【知识补充】
1、样本同时加上一个数，方差标准差不变，均值加上这个数。
2、样本同时乘以一个数，方差乘以该数的平方，标准差，均值乘以这个数。
学霸丞哥
D(x)=400 D(0.8x+20)=0.64D(x) D(x)是方差，标准差开平方
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2019-09-12 09:11:10
730以上
贴一个其它网站过来的解释（特别好的解释） 记住： 序列中每一个数都加上一个常数，标准差、方差保持不变！ 序列中每一个数乘以一个常数X，则标准差扩大X倍，方差扩大X²倍。 自己拿1，2，3，4，5套公式试试。记住就好 所以这题不管+号后面，就管乘积0.8，修正后的标准差应该是20*0.8=16
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2018-01-15 14:50:41
lealuo回复730以上
谢谢
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2018-03-08 23:58:06
冲鸭冲鸭冲鸭回复730以上
感谢！
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2018-10-15 04:10:04
700吧回复730以上
感谢！
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2018-11-30 20:12:29
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