Heather's water heater needs repair.The plumber says it will cost $300 to fix the unit,which currently costs $75 per yea
问题描述：
Heather's water heater needs repair.The plumber says it will cost $300 to fix the unit,which currently costs $75 per year to operate.Or Heather could buy a new water heater for $500,including installation and the new heated would save 60% on annual opearating costs.How long would it take for the new unit to pay for itself?
答
Assume it takes n years:In the case of having it repaired, in n years, the total cost would be: 300 + 75n dollarsIn the case of buying a new one, in n years, the total cost would be: 500 + 75(1-60%)n ...