问题如下:
Remington and Montgomery discuss Isabelle Sebastian. During a recent conversation, Sebastian, a long-term client with a $2,900,000 investment portfolio, reminded Remington that she will soon turn age 65 and wants to update her investment goals as follows:
Goal 1: Over the next 20 years, she needs to maintain her living expenditures, which are currently $120,000 per year (90% probability of success). Inflation is expected to average 2.5% annually over the time horizon, and withdrawals take place at the beginning of the year, starting immediately.
Goal 2: In 10 years, she wants to donate $1,500,000 in nominal terms to a charitable foundation (85% probability of success).
Exhibit 2 provides the details of the two sub-portfolios, including Sebastian’s allocation to the sub-portfolios and the probabilities that they will exceed the expected minimum return.
Exhibit 2 Investment Sub-Portfolios & Minimum Expected Return for Success Rate
Assume 0% correlation between the time horizon portfolios.
Using Exhibit 2, which of the sub-portfolio allocations is most likely to meet both of Sebastian’s goals?
选项:
A.The current sub-portfolio allocation.
B. A 43% allocation to sub-portfolio BY and a 57%
allocation to sub-portfolio CZ.
A 37%allocation to sub-portfolio BY and a 63% allocation to sub-portfolio CZ.
解释:
C is correct.
Goal 1 关键词:90% probability of success,20 years。通过查表,选择CZ portfolio,minimum expected return=5.7%。5.7%是名义利率,当前每年生活费$120,000会以2.5%的通货膨胀率增长,所以实际利率=(1+5.7%)/(1+2.5%)-1=3.12%.(近似法:5.7%-2.5%=3.2%也可行,计算结果影响不大。)
计算CZ的PV:由于第一笔现金流发生在0时刻,所以要使用计算器BGN模式:
输入N=20, I/Y=3.12, FV=0,PMT=120,000,得出PV=1,820,738.
Goal 2 关键词:85% probability of success,10 years。通过查表,选择BY portfolio,minimum expected return=3.6%。
计算BY的PV:将期末的$1.5m折到0时刻,得出PV=1,500,000/1.03610=1,053,158。
CZ占比:1,820,738 / 2,900,000=62.78%
BY占比:1,053,158 / 2,900,000=36.32%
所以最接近选项C。
本题理解:对于存在通货膨胀的goal 1来说,在probability=90%下的折旧率为annualized minimun expected return (5.7%)。该利率为求goal 1在目前需要多少资金投入(PV)的名义折旧率,用(1+nominal discount rate)/(1+inflation rate)-1 可以求出真实的折现率,快速的带入PMT, I/Y(真实折现),N, FV(=0), 求出PV。
这种做法可以解决很多期PMT的问题
问题:然而,这种方法在原版书课后题reading 13 的Q18中不能够适用。原版书这道题也存在有多期的PMT,这个时候的折旧率为annualized minimun expected return 却小于通胀,那么就得求出所有的PMT (Cash flows)再带入I/Y (名义折旧率)求NPV。
求问:是否解题应该先判断annualized minimun expected return 与通胀率的大小,再进行方法选择?