Question

已知各标志值减2平方的平均数为1609,标准差为3,求原平均数.

Answer 1

∑(x-2)^2/N = 1609

∑(x-e)^2/N = 9

∑(x-2)^2 -∑(x-e)^2 = 1600*N

->

N*(4-e^2) + 2*(e-2)*∑x = 1600N

同除以N

4-e^2 + 2e^2 - 4e = 1600

解得 e = 22.0749

或 e = -18.0749