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Question 1127039: A long-distance company charges $2.25 for a 6-minute call. An 12-minute call costs $3.75
a.) Write a linear function to describe the cost of a phone call in terms of the number of minutes of the call.
b.) How much would a 20-minute phone call cost?
I have no idea how to solve this. What I tried for the first part was f(x)=6x + 1.5 and I didn't have the right equation. I can't solve part B if I don't have part A right. I know how to do part B though, I just need to figure out how to get part A.
Answer by greenestamps(13200)   (Show Source):
You can put this solution on YOUR website!
A linear function is of the form y = ax+b.
When x is 0, the function value is b. On a graph, b is the y-intercept of the function.
When x increases by some amount, the function value increases by "a" times that amount. a is the slope of the line; it tells how fast the function value increases for each increase in x.
In your problem...
the function y is the cost of the call
the price increases as the number of minutes increases; the slope "a" tell you how much the cost increases for each additional minute
b tells you how much the call would cost if the call lasted 0 minutes; it is the "base" cost of the call.
To solve the problem, do the following:
(1) Find the slope, a. You know how much the cost increases for the 6 additional minutes; find the increase in cost for each minute.
(2) Using the $2.25 cost of the 6-minute call, and the slope you found in (1) above, determine what the cost would be for 0 minutes (subtract 6 times the cost-per-minute charge from the total cost of the 6-minute call). That will be the b in your linear function.
Now you have your a and b values, so you can write the function.
Now the second part is easy; simply evaluate your function for x = 20. (Or, if you understand what you are doing, you could find the cost of the 20-minute call by adding 8 times the cost-per-minute charge to the given cost of the 12-minute call.)
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