Problem 85 A portfolio management organization analyzes 70 stocks and constructs a mean-variance efficient portfolio using only these 70 securities a. How many estimates of expected returns, variances, and covariances are needed to optimize this portfolio? Estimates of expected returns Estimates of variances Estimates of covariances Total estimates b. If one could safely assume that stock market returns closely resemble a single-index structure, how many estimates would be needed? Estimates