Question

For her phone service, Mai pays a monthly fee of $19, and she pays an additional $0.04 per minute of use. The least she has been charged in a month is$70.28. What are the possible numbers of minutes she has used her phone in a month?

Answer 1

We have a phone service fee which can be divided in:

- A fixed fee of $19 per month.

- A variable fee of $0.04 per minute, so that the cost for m minutes is 0.04*m.

We can add the two fees to express the total cost in function of the minutes as:

`C(m)=19+0.04m`

For a month where the cost is C(m) = 70.28, we can calculate the minutes as:

`\begin{gathered} C(m)=70.28 \\ 19+0.04m=70.28 \\ 0.04m=70.28-19 \\ 0.04m=51.28 \\ m=(51.28)/(0.04) \\ m=1282 \end{gathered}`

Answer: if she pays at least $70.28, she has talked at least m = 1282 minutes per month.