問題：A machine has an investment cost of $60,000 at time 0. The present values (at time 0) of the expected net cash inflows from the machine over its useful life are:
　　Discount rate                          Present value of cash inflows
　　10%                                                         $64,600
　　15%                                                         $58,200
　　20%                                                         $52,100
　　What is the internal rate of return (IRR) of the machine investment?
　　A. Over 20%
　　B. Between 10% and 15%
　　C. Below 10%
　　D. Between 15% and 20%
　　答案：The correct answer is: Between 10% and 15%
　　                                                              $
　　Investment                                   (60,000)
　　PV of cash inflow                          64,600
　　NPV @ 10%                                   4,600
　　                                                             $
　　Investment                                   (60,000)
　　PV of cash inflow                         58,200
　　NPV @ 15%                                 (1,800)
　　The IRR of the machine investment is therefore between 10% and 15% because the NPV falls from $4,600 at 10% to -$1,800 at 15%. Therefore at some point between 10% and 15% the NPV = 0. When the NPV = 0, the internal rate of return is reached.