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Sunk Costs, Cost/Benefit and Payback. October 1, 2010. Sunk Costs. Problem 1:
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Sunk Costs, Cost/Benefit and Payback October 1, 2010
Sunk Costs Problem 1: Quarmby Electronics makes mobile phones. 100 000 batteries will be needed in the coming year. They can be produced in-house by two workers. The salaries of these two workers will be $50 000 each, and the cost of raw materials is $1.00 per battery. Alternatively, the batteries can be purchased from an external supplier at a unit cost of $1.90 per battery. Which option should they choose?
Sunk Costs Problem 2: Quarmby Electronics makes mobile phones. They have just invested $500 000 in a battery-making machine. This machine requires two workers to operate, and can produce 100 000 batteries per year. The salaries of these two workers will be $50 000 each. Raw materials for the batteries cost $1.00 per battery. The machine has no salvage value. Alternatively, the batteries can be purchased from an external supplier at a unit cost of $1.90 per battery. Which option should they choose?
Cost/Benefit Analysis Present worth of Benefits This is one more method of deciding between projects, commonly used by government bodies. Calculate the ratio Present worth of Costs If this is greater than one, do the project. Otherwise don’t.
As in the case of Rate of Return methods, there is a potential trap:
The government builds a bridge to Vancouver Island at a cost of $150 000 000. Each year it will cost $10 000 000 to maintain. The bridge will be a toll bridge, and is expected to bring in $20 000 000 per year in tolls. Also, the increase in tourism is estimated to be worth $5 000 000 a year in increased tax revenues. Considering a study period of 20 years and an MARR of 5%, should the project go ahead?
The government builds a bridge to Vancouver Island at a cost of $150 000 000. Each year it will cost $10 000 000 to maintain. The bridge will be a toll bridge, and is expected to bring in $20 000 000 per year in tolls. Also, the increase in tourism is estimated to be worth $5 000 000 a year in increased tax revenues. Considering a study period of 20 years and an MARR of 5%, should the project go ahead? Cost ($000 000): -150 initial cost Benefits ($000 000): Net revenue of 15 every year So B/C ratio = 15(P/A,0.05,20)/150 = 187/150 = 1.25
The government builds a bridge to Vancouver Island at a cost of $150 000 000. Each year it will cost $10 000 000 to maintain. The bridge will be a toll bridge, and is expected to bring in $20 000 000 per year in tolls. Also, the increase in tourism is estimated to be worth $5 000 000 a year in increased tax revenues. Considering a study period of 20 years and an MARR of 5%, should the project go ahead? Cost ($000 000): -150 initial cost and -10 per year Benefits ($000 000): Revenue of 25 every year So B/C ratio = 25(P/A,0.05,20)/(150 + 10(P/A,0.05,20)) = 25(12.462)/(150 + 10(12.462)) = 1.13
Fortunately, this never affects whether the B/C ratio is greater than unity. But we can’t use the size of the BC ratio to compare different projects. So once again we fall back on incremental analysis.
Example: Seven mutually exclusive plans for waste-disposal in a city have been put forward. Their costs and benefits are as follows: Option Benefit Costs P 4,000,000 500,000 Q 4,000,000 2,000,000 R 7,000,000 2,000,000 S 6,000,000 5,000,000 T 9,000,000 6,000,000 U 2,000,000 4,000,000 V 7,000,000 8,000,000 All the figures in the table are equivalent present worths, using a 25-year planning horizon and an 8% interest rate. Which alternative has the largest B/C ratio? Which is the most expensive alternative with B/C > 1? Which is the cheapest alternative with B/C > 1? Which alternative should be chosen?
Payback Period Unlike all the comparison methods discussed so far, this does not necessarily give the same result as a present worth comparison. We calculate how long the annual revenues from an initial investment take to pay off the cost of that investment. We compare this with a pre-set limit – usually between two and four years – or with the available alternatives.
Example: We replace five assembly-line workers with an industrial robot. The robot costs $300 000, and the workers earned $30 000 a year each. So payback time = 300 000/150 000 = 2 years.
Discounted Payback Period: We replace five assembly-line workers with an industrial robot. The robot costs $300 000, and the workers earned $30 000 a year each. Our MARR is 20%. 150 000(P/A,0.2,2) = 150 000(1.523) = 228 450 150 000(P/A,0.2,3) = 150 000(2.106) = 315 900 So payback period = 3 - (315 900 – 300 000)/(315 900 – 228 450) = 2.82 years.