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8. 如图是甲、乙两人 6 次投篮测试(每次投篮 10 个)成绩的统计图,甲、乙两人测试成绩的方差分别记作 $s_{甲}^{2}$、$s_{乙}^{2}$,则 $s_{甲}^{2}$____$s_{乙}^{2}$.(填“＞”“=”或“＜”)
答案
＜
9. 如果一组数据为 4,a,5,3,8,其平均数为 a,那么这组数据的方差为____.
答案
$\frac{14}{5}$
10. 为了考查甲、乙两种小麦的长势,分别从中随机抽取 10 株麦苗,测得苗高(单位:cm)如表:
| 甲 | 16 | 18 | 18 | 19 | 20 | 20 | 21 | 21 | 23 | 24 |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 乙 | 13 | 15 | 17 | 18 | 20 | 21 | 23 | 23 | 24 | 26 |
(1) 分别计算两种小麦的平均苗高;
(2) 哪种小麦的长势比较整齐? 请说明理由.
| 甲 | 16 | 18 | 18 | 19 | 20 | 20 | 21 | 21 | 23 | 24 |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 乙 | 13 | 15 | 17 | 18 | 20 | 21 | 23 | 23 | 24 | 26 |
(1) 分别计算两种小麦的平均苗高;
(2) 哪种小麦的长势比较整齐? 请说明理由.
答案
(1)甲的平均苗高是 20 cm，乙的平均苗高是 20 cm
(2) $s_{甲}^{2}=5.2$，$s_{乙}^{2}=15.8$，因为 $s_{甲}^{2}＜s_{乙}^{2}$，所以甲种小麦长得比较整齐
(2) $s_{甲}^{2}=5.2$，$s_{乙}^{2}=15.8$，因为 $s_{甲}^{2}＜s_{乙}^{2}$，所以甲种小麦长得比较整齐
