# Table shows the number of wireless service subscribers in the United States and their average monthly bill in the years from 2000 through 2015. \begin

Table shows the number of wireless service subscribers in the United States and their average monthly bill in the years from 2000 through 2015

. $$\begin{matrix} \text{Year} & \text{Subscribers} & \text{Average Monthly}\\ \text{ } & \text{(millions)} & \text{Revenue per Subscriber Unit }\\ \text{2000} & \text{109.5} & \text{48.55}\\ \text{2001} & \text{128.4} & \text{49.79}\\ \text{2002} & \text{140.8} & \text{51.00}\\ \text{2003} & \text{158.7} & \text{51.55}\\ \text{2004} & \text{182.1} & \text{52.54}\\ \text{2005} & \text{207.9} & \text{50.65}\\ \text{2006} & \text{233.0} & \text{49.07}\\ \text{2007} & \text{255.4} & \text{49.26}\\ \text{2008} & \text{270.3} & \text{48.87}\\ \text{2009} & \text{285.6} & \text{47.97}\\ \text{2010} & \text{296.3} & \text{47.53}\\ \text{2011} & \text{316.0} & \text{46.11}\\ \text{2012} & \text{326.5} & \text{48.99}\\ \text{2013} & \text{335.7} & \text{48.79}\\ \text{2014} & \text{355.4} & \text{46.64}\\ \text{2015} & \text{377.9} & \text{44.65}\\ \end{matrix}$$

One of the scatter plots suggests a linear model. Use the points at t = 0 and t = 15 to find a model in the form y = mx + b.

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The scatter plot for the subscribers suggests a linear model because the points appear to lie on a line.
Use $$(t_1,y_1)=(0,109.5)$$ and $$(t_2,y_2)=(15,377.9)$$ to find the slope:
$$\displaystyle{m}=\frac{{{y}{2}-{y}{1}}}{{{t}{2}-{t}{1}}}=\frac{{{377.9}-{109.5}}}{{{15}-{0}}}\sim{17.9}$$
Since the y-intercept is the y-value, when t=0, we know that b=109.5 from the first point. So, the equation is: y=17.9t+109.5