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Math Help - Help on Solving with System Equations

  1. #1
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    Post Help on Solving with System Equations

    Question: Suppose $10000 is invested in three different investment vehicles paying 5%, 7%, and 9% annual interest. Find the amount invested at each rate if the interest earned after 1 yr is $760 and the amount invested at 9% is equal to the sum of the amounts invested at 5% and 7%.

    My anwser:

    x + y + z = 10000
    .05x + .07y + .09z = 760
    z = ?

    Help on the third line to my answer because i have to solve.
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  2. #2
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    Re: Help on Solving with System Equations

    z=x+y
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  3. #3
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    Re: Help on Solving with System Equations

    well i have to solve using inverse matrices
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  4. #4
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    Re: Help on Solving with System Equations

    You can do that, or

    x + y + z = 10000
    .05x + .07y + .09z = 760
    z=x+y

    making a substitution

    x + y + (x+y) = 10000
    .05x + .07y + .09(x+y) = 760

    now it's two equations with 2 variables.
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