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Difference between 2 equations in percentage

  1. Jan 6, 2009 #1
    This is probably a dumb question, but I was asked to get a measurement in percentage between 2 linear equations with different slopes.

    I have the following linear equations

    y1 = 450463x + 50000
    y2 = 668453x + 100000

    Can I determine a constant difference between them, in terms of A is X percent greater than B? if so, how do I calculate it?

    my guess is :

    668453 - 450463
    ----------------- = 32.6 %

    However when I test points it doesn't work, it varies, hmm maybe I'm looking for the wrong percentage? Any ideas?
  2. jcsd
  3. Jan 6, 2009 #2


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    This is a question not a tutorial. I am moving it to the "precalculus homework" section.
  4. Jan 6, 2009 #3


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    No, you can't. The percentage difference between y1 and y2 is itself a function of x, not a constant.

  5. Jan 16, 2009 #4
    I think "a constant difference" is not exactly what you want! You need something that relates y2 with y1, correct? If so, you may obtain a linear relation between y1 and y2 (divide each equation by its slope, then subtract the two equations) you should obtain a linear equation y2 = m * y1 + b

    surely the equation describe the relation between y1 and y2. But you may do something extra
    Can you tell on what conditions one may say y2 is P% of y1? what P equals to?

    This however, is not the same as percentage difference, as HallsofIvy mentioned, the percentage difference varies according to x so it can't be constant.
    Last edited: Jan 16, 2009
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