In 1980 the average price of a home in Brainerd County was $91,000. By 1985 the average price of a home was

$111,000. Which of the following is a linear model for the price of a home, P, in Brainerd County in terms of the year, t? Let t = o correspond to


a.) P = 4000t + 91,000
b.) P = 20,000t + 91,000
c.) P = 111,000 - 20,000t
d.) P = 111,000 - 4000t

>> Let t = o correspond to ... what? 1980 ?

a.) <===== answer

if t = 0 corresponds to 1985, then

d.) <===== answer

Assuming t = 0 ==> 1980

1985 ==> t = 5
5x + 91000 = 111000
5x = 20000
x = 4000

4000 t + 91000 = P

Assuming you meant t = 0 corresponds to 1980:

You could guess and check, and you'd be able to do this fairly fast considering the answer is a), but another way of doing it would be this.
When t = 0, P = 91,000,
But when t = 5, P = 111,000, which is 91000 + 20000
This means that 5t = 20,000 because that is the only variable in the equation that could cause a rise
If 5t adds 20,000,
1t adds 4000
and from this we can gather that P = 4000t + 91000, and that the correct answer for this question is a).