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-   -   System of linear equations in 3 variables (https://www.askmehelpdesk.com/showthread.php?t=282167)

  • Nov 17, 2008, 09:05 PM
    ashy8710
    system of linear equations in 3 variables
    This question bugs me. I don't know how to get started. The teacher gave us a chart. We have to do 3 things.
    • 1. define 3 variables
      2.write system of linear equations in 3 variables relating to known quantities and variables.
      3.solve for the variables

    the chart was for dress shirts,dress slacks and suit jackets.
    it also involved cutting,sewing and packaging.
    for dress shirts
    cutting took 15 minutes
    sewing took 30 minutes
    packaging took 12 minutes
    for dress slacks
    cutting took 10 minutes
    sewing took 24 minutes
    packaging took 6 minutes
    for suit jackets
    cutting took 20 minutes
    sewing took 60 minutes
    packaging took 5 minutes
    man-hours available(hours) for all 3
    cutting took 115 hours
    sewing took 280 hours
    packaging took 65 hours
    Question to answer was how many of each of these items should you make to utilize all available man-hours of labor?

    I know the variables are x,y, and z but what would the represent and how to I make the equations.
  • Nov 19, 2008, 02:17 PM
    harum
    Everything you need is in the text of the problem. Let's consider cutting. Total cutting time is 115 hrs. This includes cutting shirts, slacks and jackets. We do not know how many of each was cut at this point, because this is what we have to find. So, let's assume the number of shirts cut is x, the number of slacks cut is y, and the number of jackets cut is z. It well may be that in the end some of the unknowns will turn out to be zero, but this is not important at this point. We just assign three variables. How many hrs does it take to cut x shirts? It is x*(1/4)hr. 15 min is 0.25 hr. How many hrs does it take to cut y slacks? y*(1/6)hr. HOw many hrs does it take to cut jackets? It is z*(1/3)hr. How long does the entire cutting job for all three items take? (1/4)x + (1/6)y + (1/3)z = 115. Here you go with your first equation. You have two more to construct, which is done similarly. Note that you use the same x, y, and z for the other two equations, because you assume that whatever was cut was also sewn and packaged. After you have three equations you solve this system of three equations to get x, y, and z. Remember that x, y, and z have to be >= 0. HTH
  • Nov 20, 2008, 03:35 PM
    rebel-2

    They are called simultaneous equations. Do a Google search for more info on how to.

    Its just the forming of the equations that are sometimes difficult

    -Cheers.
  • Dec 13, 2008, 04:46 PM
    tatianna

    x-2y+z=8
    2x+y-z=0
    3x-6y+3z=24
  • Dec 13, 2008, 05:12 PM
    galactus
    Quote:

    Originally Posted by tatianna View Post
    x-2y+z=8
    2x+y-z=0
    3x-6y+3z=24

    Please start your own thread. Do not 'hijack' another. Folks are less apt to see it than if you had your own.

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