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Math Help - Algebra

  1. #1
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    Algebra

    1. Max bought 5 notebooks and 4 pens. He spent a total of $10.65. Emily bought 3 notebooks and 3 pens for a total of $7.50. How much did the notebook and pens cost each.

    2. Mr. Smith inherits $45,000. He invests part of the money into mutal funds giving him 4% return, and he invests the other part at the stock markets giving him 6%. At the end of the year he earned $2430 of interest. How much did he invest in both accounts?

    1. This is what I did.
    -3(5n+4p=10.65)
    4(3n+3p=7.50)

    -15n -12p= -31.95
    12n +12p= 30.00
    -3/3 1.95/3

    -15n -12(.65) -31.95
    -15n - 7.80 - 31.95 I added 7.80 and divided by -15
    N=1.61 P=.65
    What did I do wrong?

    I have no idea on # 2.
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  2. #2
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    Number 2

    The solution to the second problem is :

    First create two equations...

    .04x + .06y = 2430

    and

    x + y = 45000

    solve for y in second : y = 45000 - x

    substitute this in the first equation:

    .04x + .06(45000 - x) = 2430

    .04x + 2700 - .06x = 2430

    -.02x = -270

    x = $13,500.00 at 4%

    y = 45000 - 13500 = $31,500.00 at 6%
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  3. #3
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    Quote Originally Posted by rowdy3 View Post
    1. Max bought 5 notebooks and 4 pens. He spent a total of $10.65. Emily bought 3 notebooks and 3 pens for a total of $7.50. How much did the notebook and pens cost each.

    2. Mr. Smith inherits $45,000. He invests part of the money into mutal funds giving him 4% return, and he invests the other part at the stock markets giving him 6%. At the end of the year he earned $2430 of interest. How much did he invest in both accounts?

    1. This is what I did.=====>your first part is ok
    -3(5n+4p=10.65)
    4(3n+3p=7.50)

    -15n -12p= -31.95
    12n +12p= 30.00
    ----------------------------------------------
    -3n/3 = 1.95/3
    n=.65 (The cost of one notebook)

    Substitute n=.65 into 1st equation:

    5n+4p=10.65

    5(.65)+4P=10.65 *

    3.25+4p=10.65

    4p=7.40

    p=1.85 (The cost of one pen)
    --------------------------------------------------------------
    -15n -12(.65) -31.95===>this is where you went South. You substituted the value you found for n into p. See * above.
    -15n - 7.80 - 31.95 I added 7.80 and divided by -15
    N=1.61 P=.65
    What did I do wrong?

    I have no idea on # 2.
    See corrections between the ---------------
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