Question 198154

{{{ graph( 300, 200, 0, 50, 0, 25000, -300x+24200) }}} 
y=-300x+24200

"y"= value of car at month "x"
"x"= months after purchase

ie:

The value of a certain car decreases at the rate of 300 dollars each month after being purchased new. Suppose that the car is worth 17,000 when it is 2 years old. 

17000=? -300(24)+24200
17000=? -7200+24200
17000=  17000 


Determine the value of the car after 4 years.  

y=-300(48)+24200
y=-14400+24200
y=9800


Determine how long after purchase the car's value will be half of its selling price.

By changing the formula slightly we can determine the answer easily.
We will already know the final answer, half of the original value 12100.

12100=-300x+24200
-12100=-300x
40 1/3=x

3 years, 4 months, 10 days approx.