(1)前三组数的平均数为=3,=5, ∵ | b | =x1y1+x2y2+x3y3-3• | x12+x22-32 | , ∴ | b | =2×4+3×6+4×5-3×3×5 | 22+32+42-3×32 | =, 又∵回归方程 | y | = | b | x+ | a | 必定过样本中心即(3,5), ∴5=×3+ | a | ,解得 | a | =, ∴回归直线方程是 | y | =x+; (2)后三组数据分别代入|yi-( | b | xi+ | a | )|中求解可得, |6.2-3.5-0.5×5|=0.2≤0.2, |8-3.5-0.5×6|=1.5>0.2, |7.1-3.5-0.5×7|=0.1<0.2, ∵若|yi-( | b | xi+ | a | )|≤0.2,即称(xi,yi)为(1)中回归直线的拟和“好点”, ∴拟和“好点”有2组, ∴后三组中拟合“好点”的概率P=. |