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Math Help - need help on setting up a formula

  1. #1
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    need help on setting up a formula

    Most of Conservative Casey's money was put into a savings account that
    paid 5% interest a year, but some of it was put into a risky stock fund that paid 16% a year. Casey's total initial investment in the two acounts was $10000. At the end of the first year, Casey recieved a total of $775 in interest from the two accounts. Find the amount invested in each.

    I did guess and check. Started out with 8000 and 2000 got 720 in interest. then I tried 7500 and 2500 and got the answer 775.
    Getting tired of guessing all the time. I wish I was better at algebra.

    How can I solve this with algebra?

    Vicky.
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  2. #2
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    x is the amount invested in the savings account, y is the amount invested in the risky stock, therefore...

    x+y= 10000

     1.05x+1.16y= 10775

    Can you solve these now?
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  3. #3
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    Thank you.!!!!!!!!!!!

    I see I can substitute Y for 10000 - X and then solve for X.

    Vicky.
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  4. #4
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    Or you can take a shorter route; one variable only:

    Let x = 5% amount; then 10000 - x = 16% amount
    Then:
    .05x + .16(10000 - x) = 775
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