plumber guy

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I'm having trouble with algebra...it seems like it hates me and does not want tme to pass my class.

Solve the real life problem. Ecplain your strategy.

1. A plumber charges a basic service fee plus a labor charge for each hour of service. A 2-hour job cost $120 and a 4-hour job costs $180. Find the plumbers basic charge fee.


So far all I've done is: 120/2 = 180/4
I know there should be a variable in there but I'm not sure where because 60 doesnt equal to 45.
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You have been given the two data points, (2, 120) and (4, 180). Find the equation of the straight line through these points. Evaluate at x = 0.

Eliz.
 
I'm sorry...but what? :? straight line? but if x = 0...that wouldnt be right would it?
 
You've been working on modelling with equations of the type "y = mx + b", and this question is asking you to find the equation that fits this situation.

Eliz.
 
im soooo confused...would you mind explaining in simpler terms that a beginning 8th grader might know? where would you put the variable to find the basic service fee?
 
What topics have you covered recently in class? (Since you seem to be unfamiliar with "points" and "straight lines", perhaps you're expected to take some different tack with this exercise. Knowing what you've been studying might help explain the direction in which we should be heading.)

Thank you.

Eliz.
 
well the school year has just started today and we are starting models. verbal models, algebraic models. our teacher really didnt have time to tell us how it works
 
Plumber Guy

stapel already told you that this linear equation y=mx+b; where m=(y2-y1)/(x2-x1); and (y-y1)=m(x-x1)

You have the x and y pairs (2,120), (4,180) to complete the steps above. Give it a try.
 
my teacher said to do:

Let x = labor charge per hour
Let y = basic service fee

4x-2x = 180 - 120
2x = 60
---....---
2........2

x = $30


2x + y = 120
2 (30) + y = 120
60 + y = 120
-60.........-60

y = $60


120 - 2 * 30 = 60

180 - 4 * 30 = 60


why would you do that...i dont understand
 
Why would you do which? To what step are you referring?

Eliz.
 
It looks like the educator created expressions for the hourly charge, and subtracted, since the difference would be the additional charge for the additional hours. From this, you can work backwards to the hourly charge. Once you have that, you can subtract the hourly part from the total to find the fixed service fee.

Eliz.
 
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