What are the critical factors to be observed while making (a) replacement investment decision, and (b) capital budgeting decisions under capital rationing? Do the profitability index and the NPV...

What are the critical factors to be observed while making (a) replacement investment decision, and (b) capital budgeting decisions under capital rationing? Do the profitability index and the NPV criterion of evaluating investment proposals lead to the same acceptance-rejection and ranking decisions? In what situations will they give conflicting results?