Garrett and Judy Kay are considering buying a new fridge to replace their older one. Step 2: Identify Variables and Assumptions They estimate that their current (older) fridge, which they got for free, costs them about $18 a month in electricity charges to operate. They found a new fridge that costs $1,010 to purchase and would cost only around $6 a month in electricity charges. The new fridge comes with a 10-year warranty, so they assume the new fridge to last for 10 years without any extra repair or replacement fees. If they keep their old fridge, then they assume they will need to pay around $170 sometime over the next 10 years in maintenance costs to keep it running. (For this comparison, assume they set aside the money to maintain the old fridge right at the beginning of the 10 years, even though they probably won't need the money until several years later.)