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Math Help - Help solving a algebraic system!

  1. #1
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    Help solving a algebraic system!

    I need to finish 3 or 4 problems like this tonight,


    0.4x + 0.1y = 0.28

    x+y=25


    also

    "Medication A is given every 4 hours and Medication B is given twice each day. The total intake of the 2 meds is restricted to 50.6mg per day for a patient. If the ratio of the dosage of A to B is 5 to 8, find the dosage for each administration for each medication."

    so I know the one equation is
    6x+2y=50.6

    I don't know how to do the other one...

    thanks!
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  2. #2
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    You can solve the first system of equations by substitution or by manipulating the equations and adding them.

    If you multiply both sides of the first equation by -10, you get -4x - y = -2.8. Adding this to the second equation gives you -3x = 22.2, and you can solve the system from there.


    For the second system, if the ratio of A to B is 5 to 8, then (according to your setup) x/y = 5/8, or x = 5y/8. You can substitute this value for x into the first equation in order to solve for y and then solve the system.
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  3. #3
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    Well for the first problem I get the answer x=-7.4 and y=32.4


    but it isn't really possible for x to be negattive according to the word problem since it's supposed to be a measurement of a solution
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  4. #4
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    Quote Originally Posted by emximer View Post
    Well for the first problem I get the answer x=-7.4 and y=32.4


    but it isn't really possible for x to be negattive according to the word problem since it's supposed to be a measurement of a solution
    Did you set up the equations yourself? It's possible you made an error there.
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  5. #5
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    Well I went based on what another person told me to set up which was the same as how I had it set up, but you yourself gave me an x value of -7.4

    "gives you -3x = 22.2" (from your earlier post)

    So I guess the answer is negative? Perhaps I should email my prof.

    EDIT: Heres the original problem so you can look and see if I set up the equations right

    "A biologist has a 40% solution and a 10% solution, how many cubic centimeters of each should be mixed to obtain a 25cc of a 28% solution?"
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  6. #6
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    Your first equation should be .4x + .1y = .28(25).
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  7. #7
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    Quote Originally Posted by icemanfan View Post
    Your first equation should be .4x + .1y = .28(25).
    ahh thank you so much!

    I get it now, x=15, y=10

    many thanks!

    so for my 2nd problem, I should do 2x+6y=50.6(5/8) ?
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  8. #8
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    Quote Originally Posted by emximer View Post
    so for my 2nd problem, I should do 2x+6y=50.6(5/8) ?
    No. The total amount of the dosages is equal to 50.6. The ratio relates the dosages of the two medications (x and y), but the total taken should still be 50.6.
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