3、用t检验计算。样本均值 X▔ = ( 49.6 + 49.3 + …… + 50.2 )/9 = 49.9;样本方差S^2 = E(X^2) - (EX)^2 = ( 49.6^2 + 49.3^2 + …… + 50.2 )^2/9 - 49.9^2 =0.256样本标准差 S = 0.711;计算t值 = ( X▔ - μ )/( S/√n ) = ( 50 - 49.9 )/( 0.711/3 ) =0.422t表( a = 0.05 ) = 2.310.422 < 2.31,抽样符合假设,这批大米合格;4、用置信区间计算样本均值 X▔ = ( 7.92 + 7.94 + …… + 7.94 )/9 =7.923μ0的置信区间 = X▔ ±σ/√n *Z(a/2) = 7.923 ± 0.09/3 * 1.96=7.923 ±0.059即 μ0 的置信区间为 [7.864,7.982 ],7.90在区间内。这批零件尺寸符合标准。