Quants (statistics) Question question, standard, between, correct

Elliotbay

Quick Question for you:
A Manager forecasts a bond portfolio return of 10% and estimates a standard deviation of 4%. Assuming a normal returns distribution and that the manager is correct there is:
A) 90% probability that the return will be between 3.2% and 17.2%
B) 90% probability that the return will be between 2.16% and 17.87%
C) 32% probability that the return will be between 6% and 14%
The answer is B, but the question i have is this: Why, in this case, is the standard deviation of 4% used as the standard error? I thought the standard error was s/sqrt(n)
Are the two interchangable?