Question 1176777
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The average value of a certain type of automobile was $14,520 in 1991 and depreciated to $6240 in 1995. 
Let y be the average value of the automobile in the year x, where x = 0 represents 1991. 
Write a linear equation that models the value of the automobile in terms of the year x.
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We use a linear model

    y = mx + b


for the depreciated value, starting from x = 0 at 1991.



Therefore,  y = m*0 + b = 14520  in 1991, so we just know  b= 14520.



To find m, we write

    6240 = m*4 + 14520   for the year x= 4 (1995).



From this equation, we find the slope of the linear function

    m = {{{(6240-14520)/4}}} = -2070.



So, the final expression for the depreciated value linear function is

    y = -2070*x + 14520,  or  y = 14520 - 2070x.
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Solved and explained.