不是很明白为啥要选minimum expected return来计算折现率

问题如下：

In the private wealth area, the firm has designed five sub-portfolios with differing asset allocations that are used to fund different client goals over a five-year horizon. Exhibit 3 shows the expected returns and volatilities of the sub-portfolios and the probabilities that the sub-portfolios will exceed an expected minimum return. Client Luis Rodríguez wants to satisfy two goals. Goal 1 requires a conservative portfolio providing the highest possible minimum return that will be met at least 95% of the time. Goal 2 requires a riskier portfolio that provides the highest minimum return that will be exceeded at least 85% of the time.

Exhibit3 Characteristics of Sub-portfolios

Based on Exhibit 3, which subportfolios best meet the two goals expressed by client Rodríguez?

选项：

Subportfolio A for Goal 1 and Subportfolio C for Goal 2

Subportfolio B for Goal 1 and Subportfolio C for Goal 2

Subportfolio E for Goal 1 and Subportfolio A for Goal 2

解释：

A is correct.

Goal 1 requires a success rate of at least 95%, and Subportfolio A has the highest minimum expected return (2.05%) meeting this requirement. Goal 2 requires the highest minimum expected return that will be achieved 85% of the time. Subportfolio C meets this requirement (and has a minimum expected return of 3.26%).

考点：goal-based approach

解析：Goal 1要求的成功概率为至少95%，Goal 2要求的成功概率为至少85%。95%的概率下，2.05%比1.75%，1.06%，0.25%，-0.6%都要大，所以Goal 1的highest minimum expected return为2.05%。同理，在85%的概率下， 3.26%是一行中最大的收益率，所以Goal 2的highest minimum expected return为 3.26%。它们对应的sub-portfolio是A和C。因此A选项正确。