从某项综合能力测试中抽取100人的成绩,统计如下表,则这100人成绩的平均数为______.
分数 | 5 | 4 | 3 | 2 | 1 | 人数 | 20 | 10 | 30 | 30 | 10 |
答案
由表格可以看出这100个人的成绩的平均数是
5×20+4×10+3×30+2×30+1×10 | 100 |
==3, 故答案为:3 |
举一反三
如果将一组数据中的每一个数据都加上同一个非零常数,那么这组数据的( )A.平均数和方差都不变 | B.平均数不变,方差改变 | C.平均数改变,方差不变 | D.平均数和方差都改变 | 根据台湾寿险业的资料,男性从0岁、1岁、…到60岁各年龄层的死亡率 (单位:%)依序为 1.0250,0.2350,0.1520,0.1010,0.0720,0.0590,0.0550,0.0540,0.0540,0.0520, 0.0490,0.0470,0.0490,0.0560,0.0759,0.1029,0.1394,0.1890,0.2034,0.2123, 0.2164,0.2166,0.2137,0.2085,0.2019,0.1948,0.1882,0.1830,0.1799,0.1793, 0.1813,0.1862,0.1941,0.2051,0.2190,0.2354,0.2539,0.2742,0.2961,0.3202, 0.3472,0.3779,0.4129,0.4527,0.4962,0.5420,0.5886,0.6346,0.6791,0.7239, 0.7711,0.8229,0.8817,0.9493,1.0268,1.1148,1.2139,1.3250,1.4485,1.5851, 1.7353. 经初步整理后,已知61个资料中共有24个资料小于0.2.请问死亡率资料的中位数为下列哪一个选项? (1)0.2034 (2)0.2164 (3)0.2137 (4)0.2085 (5)0.2019. | 若样本1+x1,1+x2,1+x3,…,1+xn的平均数是10,方差为2,则对样本2+x1,2+x2,2+x3,…,2+xn,下列结论正确的是( )A.平均数是10,方差为2 | B.平均数是11,方差为3 | C.平均数是11,方差为2 | D.平均数是10,方差为3 | 某射击队要从四名运动员中选拔一名运动员参加比赛,选拔赛中每名队员的平均成绩与方差S2如下表所示,如果要选择一个成绩高且发挥稳定的人参赛,则这个人应是(______). | 若数据x1,x2,x3,…,xn的平均数为5,方差为2,则数据3x1+1,3x2+1,3x3+1,…,3xn+1的平均数为______,方差为______. |
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