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Math Help - slope and y intercept help please!! Test in the morning!

  1. #1
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    Sep 2009
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    slope and y intercept help please!! Test in the morning!

    I need some help ASAP!! I SUCK at math, have a test first thing tomorrow morning... well, I'm reviewing and run into a road bump.


    Here's my problem:
    A company finds that it can produce 25 heaters for $6500, while producing 45 heaters for $9000.
    Express the cost, y, as a linear function of the number of heaters, x.

    Ok... So I've got that my points are (25,6500) and (45,9000), and I've found my slope to be 125 using the y2-y1 divided by x2-x1.

    So, I've got part of the problem solved.

    But I have to write it out as y=mx+b
    So I only have y=125x+b

    How in the heck do I find the y intercept (b)?

    My answer key says it should be 3375 but how the heck did they get that? I feel like I know this but I can't remember for the life of me! Please help if you can!!
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  2. #2
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    Joined
    Sep 2009
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    Just plug one of your two points into the equation and solve.

    y = 125x + b
    6500 = 125(25) + b Using (x,y) = (25,6500)
    6500 = 3125 + b
    3375 = b By subtracting 3125 from 6500.

    Note that you could do the exact same thing with your other point and get the same answer.
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