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 minutes of calls is , and the remaining credit after minutes of calls is . What is the remaining credit after minutes of calls?

Answer 1

Answer and Step-by-step explanation: Suppose remaining credit is y and time in minutes is x. To determine a value of y corresponding to a value of x, first find the equation for the function.

Since the function is linear, the equation is of the form: y = mx + b. To determine it:

1) Find slope, or inclination, of the line:

slope (m) = $\frac{y_{b}-y_{a}}{x_{b}-x_{a}}$

where x's and y's are points of the function.

2) Determine the y-intercept, or b: Use a point of the function, replace them at the equation, y = mx + b, and find b.

3) The equation will be: y = mx + b

With the equation, replace x for the minutes the question is asking and calculate to find the remaining credit.

Th result will be a pair (x,y)