Diane

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visits member for 2 years, 8 months
seen Jan 25 '12 at 2:48

Jan
19
comment Deriving ${\rm var}(\overline{X})$ from expected value definition
Yes! I think the biggest help was writing out Xbar - mu as the summation you have above. Then everything is quite clear. Thank you very much.
Jan
19
comment Deriving ${\rm var}(\overline{X})$ from expected value definition
E((Xbar - mu) ^ 2) = E(Xbar ^ 2 - 2 * Xbar * mu - mu ^ 2) = E(Xbar ^ 2) - 2 * mu * E(Xbar) + E(mu ^ 2) = E(Xbar ^ 2) - 2 * mu ^ 2 + mu ^ 2 = E(Xbar ^ 2) - mu ^ 2. So, I'm stuck with what to do with E(Xbar ^ 2). That's why I was thinking there is some "trick" or something I'm missing.
Jan
19
asked Deriving ${\rm var}(\overline{X})$ from expected value definition