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anonymous

  • 5 years ago

What is the value of x in the solution to the following system of equations? x+y=39 and 3x+4y=136

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  1. anonymous
    • 5 years ago
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    x=-y+39 and -4/3y+136/3

  2. anonymous
    • 5 years ago
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    x+y=39 and 3x+4y=136 -y -y -4y -4y x=38 3x= 132 /3 /3 x= 66

  3. anonymous
    • 5 years ago
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    ok thats answer

  4. anonymous
    • 5 years ago
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    kjackson

  5. anonymous
    • 5 years ago
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    that's not on the answer document

  6. anonymous
    • 5 years ago
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    what

  7. anonymous
    • 5 years ago
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    well, looking at my answers, the number could be 10,20,29,or30

  8. anonymous
    • 5 years ago
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    Take the two equations, realize that you can add and subtract the two equations from each other. What I mean by that is, you can add x + y = 39 (from the first equation) to 3x + 4y = 136 (from the second) to get 4x + 5y = 175. Now some cleverness comes into play. We want to get one of the variables to cancel. To do this we can multiply either equation by a constant. Lets multiply the first equation by 4 and subtract it from the second. 4x + 4y - (3x + 4y) = 156 - 136. When you go through and cancel you boil it down to x = 20.

  9. anonymous
    • 5 years ago
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    Oh, okay, that makes sense.

  10. anonymous
    • 5 years ago
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    You can also verify your answer if you need to do this on a test. When you arrive at a conclusion, for instance x = 20. Plug 20 in for x in one of the equations and solve for y. From equation 1 we get 20 + y = 39, which we can see y = 19. Now plugging that into equation 2 we get 3(20) + 4(19) = 136 so our answer is correct.

  11. anonymous
    • 5 years ago
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    Oh, thanks! I understand.

  12. anonymous
    • 5 years ago
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    mary100 your answer is wrong there is only one answer not to. The correct answer is x=20 it is that answer because you can solve equations by graphing x+y=39 3x+4y=136 Put your answer -x -x -3x -3x in your calc and graph y=-x+39 4y=-3x+136 it than you will see 20 divide by 4 than check your y=-3/4x+34 answer

  13. anonymous
    • 5 years ago
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    so I can do this with or without a calculator?

  14. anonymous
    • 5 years ago
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    You can do it without a calculator but the calculator just checks it

  15. anonymous
    • 5 years ago
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    Coming from someone with a B.S. in Math, you NEVER NEED a calculator, but they are often helpful.

  16. anonymous
    • 5 years ago
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    Well, I came from poor schools and back then we never got to use calculators.

  17. anonymous
    • 5 years ago
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    If you do solving equations by graphing you need a calculator but if you do elimination or substitution you totally do not need a calculator

  18. anonymous
    • 5 years ago
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    thanks, you are great!!

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