Question

The credit remaining on a phone card (in dollars) is a linear function of the total calling time made with the card (in minutes). The remaining credit after 24 minutes of calls is $21.64, and the remaining credit after 55 minutes of calls is $17.30 . What is the remaining credit after 79 minutes of calls?

Answer 1

Given data:

The credit that remains after 24 minutes is $21.64.

The credit that remains after 55 minutes is $17.30.

The expression for the equation is,

`\begin{gathered} y-21.64=((17.30-21.64)/(55-24)(x-24) \\ y-21.64=-0.14x+3.36 \\ y=-0.14x+25 \end{gathered}`

Substitute 79 for x in the above expression.

`\begin{gathered} y=-0.14(79)+25 \\ =13.94 \end{gathered}`

Thus, the credit that remains after 79 minutes is $13.94.