Engineering Economics Studying for the PE

[mkora]

I believe that thread278-163586 shows the solution, but does not account for the 10% ROI. If you look at the solution for PW = $50,000 + $50,000(P/F,i=10%,t=2) + $20,000(P/A,i=10%,t=4) - $10,000(P/A,i=10%,t=2). The last two parts of the equation that involve (P/A) are using the principle of superposition to solve for both computers maintenance cost over 4 years and then subtract out the the first 2 years when the second computer was not in service yet. Does my explanation of problem make sense to anyone else? Or am I wrong.