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Math Help - Hello, I need some help please

  1. #1
    Junior Member Rheanna's Avatar
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    Hello, I need some help please

    Question is:

    Jack has $18000 to invest , he invests 2/3 in one account and the rest in the second account. The first account returned 2% more than the second account. The total return on his investment was $1050. What were the % rates of the two accounts.

    Not sure if I'm doing it right cause I keep coming up with all sorts of answers that don't multiply to the end.

    ---------------------------------------
    |P| |R| |I|
    ---------------------------------------
    1st 12000 x (240+x)
    ---------------------------------------
    2nd 18000-12000=6000 x
    ---------------------------------------
    T= 18000 Interest saved 1050
    ---------------------------------------


    18000* 2/3 = 12000
    18000-12000= 6000
    12000*.02 = 240
    1050 -240 = 810
    810:2 = 405


    Did I set this up right? cause I keep coming up with 66.6 for x at 6000 and 33.3 for 12000

    18000-6000 %
    ---------- = -------
    18000 100

    What am I doing wrong? just doesn't look right. Thank you for the help. This is just a 5 point extra credit for class. And, I already spent 2 days on this and I'm getting frustrated. When I go to times it all to see if it adds up it doesn't. Have to be missing something.
    Last edited by Rheanna; November 1st 2008 at 06:28 PM.
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  2. #2
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    skeeter's Avatar
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    let r = base interest rate as a decimal

    $12000(r+.02) = 12000r + 240

    $6000(r) = 6000r

    18000r + 240 = 1050

    solve for r ... remember it is the base interest rate in decimal form
    Last edited by skeeter; November 2nd 2008 at 03:57 AM. Reason: lost a zero ... fixed same
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  3. #3
    Junior Member Rheanna's Avatar
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    I did all that didn't I? I got the same answers up there.
    Last edited by Rheanna; November 1st 2008 at 09:03 PM.
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  4. #4
    Junior Member Rheanna's Avatar
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    came up with 15.5% hmm
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  5. #5
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    I lost a zero when I got up to let the dogs out ... it's fixed. Take another look at my previous post.
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  6. #6
    Junior Member Rheanna's Avatar
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    Quote Originally Posted by skeeter View Post
    let r = base interest rate as a decimal

    $12000(r+.02) = 12000r + 240

    $6000(r) = 6000r

    18000r + 240 = 1050

    solve for r ... remember it is the base interest rate in decimal form
    12000r+240+600r=1050
    -240
    -----------------------
    18000r=810

    810/18000
    r=0.045%

    Is that wrong? I'm in Elementary Algebra.
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  7. #7
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    r = .045 = 4.5%
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  8. #8
    Junior Member Rheanna's Avatar
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    but when you do the total like mutiply it across it doesn't add up

    18000(.045)=1050 =810 probably be for the 6000 loan have to divide that by 2 you get 405 then you add the 240 to 405 you 625 for the 1200 loan

    so then I would need to do it for 12000 to find that percent%


    when you do the tic tac toe box doesn't it have to add down to 1050 and then multiply with everything across to add to 1050

    that's how I've been doing it.
    Last edited by Rheanna; November 2nd 2008 at 09:57 AM.
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  9. #9
    MHF Contributor
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    r = 4.5% = .045

    r + 2% = 6.5% = .065

    12000(.065) + 6000(.045) = ?
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  10. #10
    Junior Member Rheanna's Avatar
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    Quote Originally Posted by skeeter View Post
    r = 4.5% = .045

    r + 2% = 6.5% = .065

    12000(.065) + 6000(.045) = ?

    oh ok I forgot about the 2% maybe that's where I was messing up.

    sorry for being a pain..

    so when you add .065 +.045 you get .11 % as a total

    12000 ----------------.065%---------------.065(240+540)=780
    _______________________________________________

    6000 18000-12000
    =6000 ----.045%------------ 6000(.045)= 270
    --------------------------------------------------------

    Total= 18000--------------.11%----------------1050

    Total=18000(.11)=1050

    It add downs but it isn't multiplying across

    Does not add up? Percent wise anyway, comes to 1980 and not 1050 When I mutiply across. That's what I mean. sorry... I don't know how to do the math computer code.
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  11. #11
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    so when you add .065 +.045 you get .11 % as a total
    you do not add the two percents ... one percent (6.5%) is applied only to the $12000, the other (4.5%) only applies to the remaining $6000.

    12000(.065) + 6000(.045) = 1050

    if you want to find the "effective" total interest ...

    \frac{1050}{18000} = .0583 \approx 5.8%

    you're done.
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  12. #12
    Junior Member Rheanna's Avatar
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    Quote Originally Posted by skeeter View Post
    you do not add the two percents ... one percent (6.5%) is applied only to the $12000, the other (4.5%) only applies to the remaining $6000.

    12000(.065) + 6000(.045) = 1050

    if you want to find the "effective" total interest ...

    \frac{1050}{18000} = .0583 \approx 5.8%

    you're done.

    oh ok I always thought you had to add them in the total slot then times it to the 18000 to get the 1050. Thank you, hun I appreciate it.
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