金键学生奶的平均数=(2+1+0+1+0+9+8)÷7=3,方差S12=[(2-3)2+(1-3)2+(0-3)2+(1-3)2+(0-3)2+(9-3)2+(8-3)2]=12.57; 金键酸牛奶的平均数=(70+70+80+75+84+81+100)÷7=80,方差S22=[(70-80)2+(70-80)2+(80-80)2+(75-80)2+(84-80)2+(81-80)2+(100-80)2]=91.71; 金键原味奶的平均数=(40+30+35+30+38+47+60)÷7=40,方差S32=[(40-40)2+(30-40)2+(35-40)2+(30-40)2+(38-40)2+(47-40)2+(60-40)2]=96.86; (1)学生奶=3,酸牛奶=80,原味奶=40,金键酸牛奶销量高;
(2)12.57,91.71,96.86;
(3)金键学生奶销量最稳定. |