一組數(shù)據(jù)3,4,5,5,8的方差是 .
【答案】
分析:根據(jù)方差的公式計算.方差S
2=

[(x
1-

)
2+(x
2-

)
2+…+(x
n-

)
2].
解答:解:數(shù)據(jù)3,4,5,5,8的平均數(shù)為

=5,
故其方差S
2=

[(3-5)
2+(4-5)
2+(5-5)
2+(5-5)
2+(8-5)
2]=2.8.
故填2.8.
點評:本題考查方差的定義與意義:一般地設n個數(shù)據(jù),x
1,x
2,…x
n的平均數(shù)為

,則方差S
2=

[(x
1-

)
2+(x
2-

)
2+…+(x
n-

)
2],它反映了一組數(shù)據(jù)的波動大小,方差越大,波動性越大,反之也成立.