NO.PZ2015120601000010
问题如下：
At the end of the current year, an investor wants to make a donation of $20,000 to charity but does not want the year-end market value of her portfolio to fall below $600,000. If the shortfall level is equal to the risk-free rate of return and returns from all portfolios considered are normally distributed, will the portfolio that minimizes the probability of failing to achieve the investor’s objective most likely have the:
选项：
解释：
C is correct.
The portfolio with the highest safety-first ratio minimizes the probability that the portfolio return will be less than the shortfall level (given normality). In this problem, the shortfall level is equal to the risk-free rate of return and thus the highest safety-first ratio portfolio will be the same as the highest Sharpe ratio portfolio.
这道题仍然是要从公式入手，SFR公式为 SFR=[E(Rp) – RL ] / σp 。所以可以看出，当threshold / minimum return 也就是RL被设定为 risk free return Rf时，这个公式恰好就等于Sharpe Ratio（SR）。所以SFR等于SR是有前提的。
Shortfall risk是SFR里Rp低于RL的风险(就是投资的收益率低于了最低要求的门槛收益率的风险)。所以要让shortfall risk最小，相当于让SFR最大，也就是让E(Rp)尽量的大于RL。由于这道题RL=Rf，所以也相当于让SR最大。
請問因爲RL=Rf，SFR等於0? 所以是highest safety-ratio 以及highest sharp ratio?
