24. We know the total portfolio value and the investment of two stocks in the portfolio, so we can find
the weight of these two stocks. The weights of Stock A and Stock B are:
Since the portfolio is as risky as the market, the of the portfolio must be equal to one. We also know the
of the risk-free asset is zero. We can use the equation for the of a portfolio to find the weight of the
third stock. Doing so, we find:
Solving for the weight of Stock C, we find:
So, the dollar investment in Stock C must be:
We also know the total portfolio weight must be one, so the weight of the risk-free asset must be one
minus the asset weight we know, or:
So, the dollar investment in the risk-free asset must be:
Challenge
25. We are given the expected return of the assets in the portfolio. We also know the sum of the weights
of each asset must be equal to one. Using this relationship, we can express the expected return of the
portfolio as:
E(RP) = .1360 = wX(.1140) + wY(.0868)
And the weight of Stock Y is: