Variance of a lognormal

[DITmoonlight]

This is kind of a silly question but I just want to make sure...

Since the variance of a lognormal is (e^sigma^2 -1)e^2mu+sigma^2,

If I get a question to solve the variance of a lognormal and i have sigma, do I raise e to the variance or do I multiply sigma by 2 since it's a power of a power?

[daaaave]

You raise e to the variance. Adding parentheses, I get

Var X = \left[\exp(\sigma^2) -1 \right]\exp\left(2 \mu + \sigma^2\right)

for X=e^Z, \qquad Z \sim N(\mu, \sigma^2)

[DITmoonlight]

I thought so but I wasn't sure since I didn't have any problems about it in my book.
Thanks again Dave!

[bmifsud]

How do you figure out mu there?

[bmifsud]

Can someone explain how you found mu here?

[Actuarialsuck]

What do you mean how? If you are not given it? There's various techniques you will learn on course 4, MoM, MLE, etc. (assuming you are given data to estimate it from)