Final answer:
To determine when John can shop for a new freezer, we calculate his average cost of owning the freezer by adding the purchase price and annual operating cost, dividing by the number of years.
John can shop for a new freezer at the beginning of the 12th year, after the average cost drops below $117 per year.
Step-by-step explanation:
To determine when John can shop for a new freezer, we need to calculate the average cost of owning the freezer until it drops below $117. The initial purchase price of the freezer is $850, and the annual operating cost is $40.
The average cost per year (AC) can be calculated using the formula:
AC = (Initial Purchase Price + Total Operating Costs) / Number of Years
To find out in which year (n) the average cost will be less than $117, we can set up the inequality:
850 + 40n < 117n
Solving for n gives:
n > 850 / (117 - 40)
Which simplifies to:
n > 850 / 77
Calculating the exact value gives:
n > 11.03
So, John can start shopping for a new freezer after 11 full years, but since we need to round to the nearest month, we have to consider how many months into the 12th year the average cost becomes less than $117.
To calculate that, we take the decimal part .03 and multiply by 12 to get the number of months (m):
m = 0.03 '' 12
Thus:
m = 0.36 month
Since we can't have a fraction of a month, and rounding 0.36 to the nearest month is 0, John can start shopping for a new freezer right at the beginning of the 12th year.