Chapter 1.1, Problem 21E

a.

To determine

To graph: The number N $\left(\text{in millions}\right)$ of US cellular phone subscribers as a function of t $\left(\text{years}\right)$ with the given data is as below,

t	1996	1998	2000	2002	2004	2006
N	44	69	109	141	182	233

Explanation of Solution

Given information:

The number N $\left(\text{in millions}\right)$ of US cellular phone subscribers is shown in the table.

t	1996	1998	2000	2002	2004	2006
N	44	69	109	141	182	233

Graph:

The graph of N vs t can be drawn by using t as x-axis and N as y-axis. The obtained graphs is as like this,

  

Interpretation:

The obtained graph shows that the number of US cellular phone subscribers are continuously increasing from 1996 to 2006.

b.

To determine

To calculate: The estimation of the number of cell-phone subscribers at midyear in 2001 and 2005, Using the given graph.

  

Answer to Problem 21E

The estimated numbers of cell-phone subscribers at the midyear 2001 are 125 millions and at the midyear 2005 are 207.5 millions.

Explanation of Solution

Given information:

The number N $\left(\text{in millions}\right)$ of US cellular phone subscribers is shown in the table.

t	1996	1998	2000	2002	2004	2006
N	44	69	109	141	182	233

Calculation:

Consider the given graph, the year 2001 lies in between 2000 and 2002 on the x-axis. Now, take the corresponding value of y with respect to x as 2001, it is find out to be 125 on this graph.

Similarly, the year 2005 lies in between 2004 and 2006 on the x-axis. Now, take the corresponding value of y with respect to x as 2005, it is find out to be 207.5 on this graph.

  

Therefore, the estimated numbers of cell-phone subscribers at the midyear 2001 are 125 millions and at the midyear 2005 are 207.5 millions.