Chapter 11.1, Problem 57E

The bar graph shows the average number of hours per day that US. adult users spent on digital media (desktop/laptop, mobile, and other devices) from 2008 through 2014.

Let $a_n$ represent the average number of hours per day that US. adult users spent on digital media $n$

years after 2007.

a. Use the numbers given in the graph to find and interpret $\frac{1}{7}{\displaystyle \underset{i=1}{\overset{7}{\sum }}{a}_i}$. Round to the nearest tenth of an hour.

b. The finite sequence whose general term is

$a_n=0.5n+2,$

where $n=1,2,3,4,5,6,7,$ models the average number of hours per day that US. adult users spent on digital media $n$ years after 2007. Use this model to find $\frac{1}{7}{\displaystyle \underset{i=1}{\overset{7}{\sum }}{a}_i}$. Does this underestimate or overestimate the rounded value you obtained in part (a)? By how much?