a Begin by writing an equation that represents the average cost. Then, use the trace feature of your graphing calculators.
B
b Use the table feature of your graphing calculators.
A
a 10 months
B
b The average cost approaches $59
Practice makes perfect
a We will begin by writing an equation that represents the average cost. Let y be the average cost and x be the number of months.
Verbal Expression
Algebraic Expression
Initial cost ($)
100
Cost for x number of monts ($)
59 x
Total cost ($)
59 x+100
Average cost is $y.
y=59 x+100/x
Therefore, we have the equation.
y=59x+100/x
Next we will graph the equation. To draw a graph on our calculator, we first have to press Y= and write the function on one of the rows. Having written the function, we can press GRAPH to draw it.
To observe the graph properly, we can set the viewing window as shown below.
Now, we press TRACE and then use the right and left arrow keys to move along the graph to get y≈ 69.
The average cost falls to $69 per month when we purchase 10 months of membership.
b To examine the average cost as the number of months increases, we will use the table feature of our graphing calculator. We will first change the table settings as below by pushing 2ND and WINDOW.
Now, we will push 2ND and GRAPH to see the table.
The table shows that the average cost approaches $59 as the number of months increases.
