Chapter 3.5, Problem 80E

Applications

Cell phone bills A phone company charges $\$11$ per month plus a nickel per call.

a. Find a rational function that expresses the average cost $f\left(x\right)$ of a call in a month when $x$ calls were made.

b. To the nearest tenth of a cent, find the average cost of a call in a month when $68$ calls were made.

c. Find the inverse of the function found in a part (a) to find a formula that gives the number of calls ${\mathrm{f}}^{-1}\left(\mathrm{x}\right)$ that can be made for an average cost $x$.

d. How many calls need to be made for an average cost of $15\cancel{c}$ per call?