In desalting groundwater that contains a signifi­cant amount of sulfates, the concentrate that is generated during the desalting process can some­times be tough on equipment, so the equipment’s useful life is uncertain. For a treatment train that has an initial cost of $90,000 and an estimated operating cost (OC) between $15,000 and $20,000 per month, use a spreadsheet to deter­mine how many months the equipment must last to recover the investment at i = 0.5% per month at each OC value? Assume the income from the sale of calcium sulfate is $22,000 per month. (Note: Solve using increments of $1000 OC per month.)

Question

What will be an ideal response?

Answer 1

Let np = number of months. Sample relation for equivalent worth per month for

$15,000 OC is: = - PMT(0.5%,$D3,-90000,) + 22000 - $A3



Apply Goal Seek for each OC estimate to set equivalent worth to zero and display the

respective np value.