题目

工程经济学一道题~
The three alternatives described below are available for supplying a community water supply for the next 50 years when all economic lives,as well as the period of analysis,terminates.
Cost Project A Project B Project C
Construction Cost
Year 0 $20,000,000 $10,000,000 $15,000,000
Year 20 0 $10,000,000 $12,000,000
Year 35 0 $10,000,000 0
Maintenance Cost
Years 1 - 20 $70,000 $40,000 $60,000
Years 21 - 35 $80,000 $70,000 $80,000
Years 36 - 50 $90,000 $90,000 $90,000
Determine which project is preferred using the present worth method.Assume an interest rate of 4.5%.
以前没学过 这是另一门课的题.用present worth method
排版有点乱，费用是3个工程排在一起 工程a的建设费用是0年$20,000,000，后面2个阶段都是0.工程b是3个阶段开始都投资$10,000,000，工程c是第35年是0.

提问时间：2021-03-31

答案

应该是分别求三个工程的净现值NPV,画出相应的现金流量图就OK了
我列出工程a的计算式子,其他两个类似的,最后比较三个NPV的大小,去最小的那个.
NPV（a）=20,000,000+70,000*(P/A,4.5%,20)+80,000*(P/A,4.5%,15)*(P/F,4.5%,20)+90,000*(P/A,4.5%,15)*(P/F,4.5%,35)