How is the expected rate of return (ERR) calculated?

Is an investor expected to earn the ERR of 12.5% in any given year?

In statistics, the value (n-1), with n being the number of observations, is commonly used in the standard

deviation formula when the sample size is small. This formula states that the standard deviation is equal to the square root of the summation of the squared deviations divided by n-1. Why does Mark not include (n-1) in his calculation of standard deviation?

Explain the calculation of standard deviation as it applies to this problem.

What is the standard deviation of this problem if the probability of a great economy changes to 40% and the probability of a good economy changes to only 20%?