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11. Electrical power costs at a mine are estimated to be $850,000 in each of the next 12 years. Determine the present value of this expenditure at an interest rate of 12% 12. Tenders received from manufacturers indicate that a fan priced at $150,000 will cost $220,000 per year to run, whilst a fan costing $265,000 will require $190,000 per year in operating costs. If the costing period is five years with an annual interest rate of 10%, determine which fan is the most economical. 17AA mine shaft is to be sunk at a cost of $200 million. The life of the shaft is estimated to be 25 years during which time the average planned rate of mineral production is 2.6 million tonnes per year. If the annual interest rate is 6%, determine i The equivalent annual cost of the shaft in S per year i. Corresponding production cost in s per tonne mined 18. An underground airway is driven at a capital cost of $1.15 million. In its eight year life it is planned to pass an airflow of 1080 m3/s at a frictional pressure drop of 720 Pa. The main fans operate at an efficiency of 87%. The annual interest rate is 7% and the average cost of power is $1.25 per kWh, determine the annual cost of owning and operating the airway. (Hint air power = pressure x air quantity) 19. How can inflation and risk factor be accounted in a standard discounted cash flow analysis