Example 10 in reading 18 on the CEFA endowment.

I have read through the explanation many times and I am still not sure why we do *not* use Portfolio 5 to calculate adjacent Corner Portfolios. In Example 9 (the BlueBox right before this question) we clearly used the two adjacent corner portfolios. In texample 10, they use one of the risky portfolios above the required rate of 6.5% and the risk-free rate. Why the risk-free rate? The case clearly says that “Exhibit 19 gives results from the **sign-constrained MVO** based on the inputs in Exhibit 18.” IF it is sign-constrained that means no shorting is allowed so why do they use the risk-free rate and omit Portfolio 5?

The solution says “Note that we need not consider the portion of the efficient frontier beginning at and extending below Corner Portfolio 5, because the portfolios on it do not satisfy CEFA’s 6.5 percent return objective”. The whole point of mixing two corner portfolios is to BLEND them in order to get the most mean-optimized average portfolio given a return requirement. We did the same thing in Example 9.

I even worked out the weights of Corner Portfolio 4 and 5’s standard deviations and the combined weighted value is still under the 12% standard deviation.

Can someone please have a look at this and tell me what I am missing? Did something miraculously change from Example 9 to Example 10?