Which equation could be used?

Question

A landscaper buys a new commercial-grade lawn mower that costs $2800. Based on past experience he expects it to last 8 years and then he can sell it for scrap metal with a salvage value of about $240. Assuming the value of the lawn mower depreciates at a constant rate, which equation could be used to find its approximate value after x years, given that x<8?

Answer 1

The new value of the lawn mower is $2800, the value after 8 years is $240. The depreciation over this time is 240 - 2800 = $-2560. Dividing by 8, you have the rate of depreciation:

 

m = -2560/8 = -320 dollars/year.

 

Use the slope-intercept equation of a line to get the formula. Here, b = 2800; so the equation is

 

y = -320x + 2800, x < 8.

 

Notice that x = 0 gives 2800 and x = 8 gives 240, which were given in the problem.