Skip to content

Log of the mean of a standard lognormal

Question

If ln⁡X\ln X has a standard normal distribution, what is the value of ln⁡(E[X])\ln\left(\mathbb{E}[X]\right)?

Short answer

1/21/2. Write X=eZX=e^Z with Z∼N(0,1)Z\sim N(0,1). The normal moment generating function gives E[eZ]=e1/2\mathbb{E}[e^{Z}]=e^{1/2}, so the log of the mean is 12\tfrac12 (not 00, which is the mean of the log).

Adapted from QuantQuestions.io; question and answer rewritten by SelfMadeQuant.com.

See the hint and the full worked solution in the question bank (free account).

Open the worked solution

Lessons behind this question

Start with a free lesson: Normal Distribution is part of a free topic. Create a free account, no card needed, to read it in full with worked solutions.

Read it free