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Math Help - Help on an investment prob. pleasee

  1. #1
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    Help on an investment prob. pleasee

    Hey guys new to this forum, and not real good with math. But i really like it, and hope to get better as time goes on

    But heres the problem: A broker invested $24,000 in two mutual funds, one earning 9% annual interest and the other earning 14%. After 1 year, his combined interest is $3,135. How much was invested at each rate?

    Can anyone give me a nice forumula i can use for this prob., including an answer? thankyou so much!!
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  2. #2
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    Hello, Baginoman!

    Welcome aboard!

    There is no nice formula for this,
    . . but we can think our way through it.


    A broker invested $24,000 in two mutual funds,
    one earning 9% annual interest and the other earning 14%.
    After 1 year, his combined interest is $3,135.
    How much was invested at each rate?

    Let x = amount invested at 9%.
    Then 24,000 - x = amount invested at 14%.

    He invested x dollars at 9%.
    . . The interest is: . 0.09x dollars.

    He invested 24,000 - x dollars at 14%.
    . . The interest is: . 0.14(24,000-x) dollars.

    Hence, his total interest is: . 0.09x + 0.14(24,000 - x) dollars.

    But we are told that his total interest is \$3,135.


    There is our equation! . . . 0.09x + 0.14(24,000-x) \;=\;3135


    Got it?

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  3. #3
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    well i kinda got the same forumula, but the wrong answer from the book? haha

    so if its: .09x + 3,360 - .14x = 3,135(subtracting .09 from both sides)=>

    3,360 - .23x = 3135(Subtracting 3,360 to the other side)=>

    -23x = .225(divide)= $978?

    I get totally diff answer from the book
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  4. #4
    MHF Contributor ebaines's Avatar
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    Quote Originally Posted by Baginoman View Post
    well i kinda got the same forumula, but the wrong answer from the book? haha

    so if its: .09x + 3,360 - .14x = 3,135(subtracting .09 from both sides)=>

    3,360 - .23x = 3135(Subtracting 3,360 to the other side)=>

    -23x = .225(divide)= $978?

    I get totally diff answer from the book
    Your first step above is incorrect - you don't need to subtract .09x from both sides, becuase there is no .09x on the right had side. Start out by combining like terms:

    .09x + 3,360 -.14x = 3,135
    (.09x-.14x) = 3135-3360
    -.05x = -225
    x = 4,500.

    Some advice: always double check your answers. In your case when you got x = 978, if you plug that back into the original equation you would have:

    .09*978 + 3,360 -.14*978 = 3,135
    88+3,360-137 = 3,135
    3,311 = 3,135

    Clearly something is not right with x= 978, so you would know to go back and look for an error in your work. Hope this helps.
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