Question

1.Suppose a refrigerator that sells for $700 costs $85 a year for electricity. Write an expression for the cost to buy and run the refrigerator for x years.

2.Suppose another refrigerator sells for $1000 and costs $25 a year for electricity. Write an expression for the total cost for this refrigerator over x years.

3.Over 10 years, which refrigerator costs the most? By how much?

4.In how many years will the total costs for the two refrigerators be equal?

Answer 1

1) cost of refrigerator = $ 700

cost of electricity = $ 85 / year

expression for the cost

C(x) = 85x + 700

2) expression for another refrigerator is

C(x) = 25x + 1000

3) cost of 1st refrigerator over 10 years is 85(10) + 700

= $ 1550

cost of 2nd refrigerator over 10 years is 25(10) + 1000

= $ 1250

so, cost of 1st refrigerator is more by $ 300

4) setting the two costs equal to each other

85x + 700 = 25x + 1000

x = 5

so, after 5 years the cost of two refrigerators will be equal