Chapter 1.1, Problem 3GP

To determine

To write an expression to find the cost for $40$ calls during one month. The find the cost for $40$ calls during one month. Make a table showing the cost for $40,50,60$ and $70$ calls.

Answer to Problem 3GP

Expression to find the cost for $40$ calls during one month is $15+0.25\left(40\right)$ .

Table showing the cost is

Number of calls (x)	Cost during month ($)
40	25
50	27.5
60	30
70	32.5

Explanation of Solution

Given information: A company offers a plan where they charge $\$15$ per month and $\$0.25$ for each call made or received

Formula Used:

Slope intercept form of line is $y=mx+c$ , where

$m=$ Slope of graph of equation

$c=$ y-intercept of graph of equation

Calculation:

Given that a company offers a plan where they charge $\$15$ per month and $\$0.25$ for each call made or received

Let the number of calls made or received be $x$ and the cost during one month be $y$

Thus, the equation is given as

$y=15+0.25x$

Now, number of calls made or received during one month, $x=40$

Hence, the expression will become

$y=15+0.25\left(40\right)$

On evaluating, cost is

$\begin{array}{l}y=15+10\\ y=25\end{array}$

Thus, cost for $40$ calls during one month is $\$25$

When $x=50$

$\begin{array}{l}y=15+0.25\left(50\right)\\ y=15+12.5\\ y=27.5\end{array}$

When $x=60$

$\begin{array}{l}y=15+0.25\left(60\right)\\ y=15+15\\ y=30\end{array}$

When $x=70$

$\begin{array}{l}y=15+0.25\left(70\right)\\ y=15+17.5\\ y=32.5\end{array}$

Thus, the table is

Number of calls (x)	Cost during month ($)
40	25
50	27.5
60	30
70	32.5

Conclusion:

Hence, the expression to find the cost for $40$ calls during one month is $15+0.25\left(40\right)$ .