SOLUTION: The cost of a new math textbook was $80 in 2005. It went up to $120 in 2010. Assuming the cost increases linearly, write an equation representing the cost as a function of time.

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Question 323799: The cost of a new math textbook was $80 in 2005. It went up to $120 in 2010. Assuming the cost increases linearly, write an equation representing the cost as a function of time.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
You need a linear equation, which has the form
C+=+m%2Ay+%2B+b
C = cost of a textbook during a particular year
y is a particular year, calling
2005+=+0
2006+=+1
2007+=+2
etc.
All you have to do is find b and m in the equation
m is the slope, or rate of increase
When y increases from 0 to 5 (2005- 2010),
C increases from 80 to 120
The slope is (change in C)/(change in y)
m+=+%28120+-+80%29%2F5
m+=+40%2F5
m+=+8
So far the equation is
C+=+8y+%2B+b
Now to find b,
Use C+=+120, and y+=+5 (a point on the line)
120+=+8y+%2B+b
120+=+8%2A5+%2B+b
b+=+120+-+40
b+=+80
So, the equation is
C+=+8y+%2B+80
The plot of this equation is:
+graph%28+700%2C+500%2C+-5%2C+15%2C+-50%2C+200%2C+8x+%2B+80%29+