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.

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) (Show Source): You can put this solution on YOUR website!
You need a linear equation, which has the form

= cost of a textbook during a particular year
is a particular year, calling

etc.
All you have to do is find and in the equation
is the slope, or rate of increase
When increases from to (2005- 2010),
increases from to
The slope is (change in C)/(change in y)

So far the equation is

Now to find ,
Use , and (a point on the line)

So, the equation is

The plot of this equation is:

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