Problema Solution
Suppose that the credit remaining on a phone card (in dollars) is a linear function of the total calling time (in minutes). When graphed, the function gives a line with a slope of -.13
There is 27.99 in credit remaining on the card after 23 minutes of calls. How much credit will there be after minutes of calls?
Answer provided by our tutors
From the given information, we know that the equation of our line is in the general form y=mx+b where x is time (in min), m is slope, y is credit (in dollars) and b is the intersection on the y (time) axis. We also know that the slope is -.13. Therefore, we can write:
y=-.13x+b
Then we are given x=23min and y=27.99. Therefore, we can find 'b', using:
27.99=-.13(23)+b
b=25
Therefore, we can write the general equation:
y=-.13x+25
After 'x' minutes of calls, there will be 'y' credit remaining.