已知一個樣本91,89,88,90,92,則這個樣本的方差是 .
【答案】
分析:根據方差公式計算即可.方差S
2=
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[(x
1-
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)
2+(x
2-
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)
2+…+(x
n-
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)
2].
解答:解:這組樣本的平均值為
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=
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(91+89+88+90+92)=90
方差S
2=
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[(91-90)
2+(89-90)
2+(88-90)
2+(90-90)
2+(92-90)
2]=2,
故答案為:2.
點評:本題考查了方差的定義.一般地設n個數據,x
1,x
2,…x
n的平均數為
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,則方差S
2=
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[(x
1-
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)
2+(x
2-
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)
2+…+(x
n-
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)
2],它反映了一組數據的波動大小,方差越大,波動性越大,反之也成立.