Question

The graph below shows the total cost of cable service to new customers for the 1st 5 months based on the data in the graph of which of the following expressions can be used to represent the total cost of cable service for M months?

Answer 1

First, we find the slope using the following formula

`m=(y_2-y_1)/(x_2-x_1)`

Let's replace the points (1,10) and (5, 170) where

`\begin{gathered} x_1=1 \\ x_2=5 \\ y_1=10 \\ y_2=170 \end{gathered}`
`m=(170-10)/(5-1)=(160)/(4)=40`

Then, we use the point-slope formula to find the equation

`\begin{gathered} y-y_1=m(x-x_1) \\ y-10=40(x-1) \\ y-10=40x-40 \\ y=40x-40+10 \\ y=40x-30 \end{gathered}`

Hence, the answer is D where x is M.