Corner portfolios exactly, total, example, required, return

Zesty

I have a knack of doing exactly the wrong thing in these return calculations:

example:

in 2008 Morning CFAI , they give a return requirement and say there are expenses as well. Ok. So to get the total required return would you add or geometrify the required return and the expense?

Turns out if you the geometric , the constraint on Stdev is not met, and the answer if wrong.

So by doing the right thing ( IMO only ) you get the wrong answer.

Conversely to get to the right answer , suspend your judgement and do the wrong thing . Thing is how do I guess when to do the wrong thing?