计算平均值：（36.2+38.8+41.8）=38.933
计算标准差(36.2−38.933)2≈(−2.733)2≈7.469
(38.8−38.933)2≈(−0.133)2≈0.018
(41.8−38.933)2≈(2.867)2≈8.218
平方和：7.469+0.018+8.218=15.705
计算标准差=