Many Wall Street firms use LP models to select a desirable bond portfolio. The following is a simplified version of such a model. Solodrex is considering investing in four bonds; $1 million is available for investment. The expected annual return, the worstcase annual return on each bond, and the “duration”

of each bond are given in the file P04_56.xlsx. (The duration of a bond is a measure of the bond’s sensitivity to interest rates.) Solodrex wants to maximize the expected return from its bond investments, subject to three constraints:

■ The worst-case return of the bond portfolio must be at least 8%.

■ The average duration of the portfolio must be at most