State Probability Return on Stock A Return on Stock B

1 0.10 10% 8%

2 0.20 13% 7%

3 0.20 12% 6%

4 0.30 14% 9%

5 0.20 15% 8%

Which of the following portfolio(s) is(are) on the efficient frontier? A. The portfolio with 20 percent in A and 80 percent in B. B. The portfolio with 15 percent in A and 85 percent in B. C. The portfolio with 26 percent in A and 74 percent in B. D. The portfolio with 10 percent in A and 90 percent in B. E. A and B are both on the efficient frontier.

Here is the answer, but I don't understand how they got it:

The Portfolio's E(Rp), sp, Reward/volatility ratios are 20A/80B: 8.8%, 1.05%, 8.38; 15A/85B: 8.53%, 1.06%, 8.07; 26A/74B: 9.13%, 1.05%, 8.70; 10A/90B: 8.25%, 1.07%, 7.73. The portfolio with 26% in A and 74% in B dominates all of the other portfolios by the mean-variance criterion.