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GRE数学题,麻烦大神们帮我看一下SetXconsistsof100numbers.Theaverage(arithmeticmean)ofsetXis10,andthestandarddeviationis4.6.Whichofthefollowingtwonumbers,whenaddedtosetX,willdecreasetheset’sstandardd
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GRE数学题,麻烦大神们帮我看一下
Set X consists of 100 numbers. The average (arithmetic mean) of set X is 10, and the standard deviation is 4.6. Which of the following two numbers, when added to set X, will decrease the set’s standard deviation by the greatest amount?
-100 and -100
-10 and -10
0 and 0
0 and 20
10 and 10
Set X consists of 100 numbers. The average (arithmetic mean) of set X is 10, and the standard deviation is 4.6. Which of the following two numbers, when added to set X, will decrease the set’s standard deviation by the greatest amount?
-100 and -100
-10 and -10
0 and 0
0 and 20
10 and 10
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答案和解析
必须是10和10啊,方差是[(X1-平均)^2+(X1-平均)^2......+(X100-平均)^2]/100如果增加X101=10和X102=10,分母上面的和不变,因为(X101-平均)^2+(X102-平均)^2=0+0=0,而分母变成了102,所以除得的数值就会变小。如...
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