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-   -   Quadratic Equation involving money (https://www.askmehelpdesk.com/showthread.php?t=446416)

  • Feb 12, 2010, 06:52 PM
    HuiLi
    Quadratic Equation involving money
    A trader bought some paraffin for $500.He paid $x for each litre of paraffin.
    Qn:
    a)Due to a leak,he lost 3 litres of paraffin.He sold the remainder of the paraffin for $1 per litre more than he paid for it.Write down an expression,in terms of x,for the sum of money he received.
    b)He made a profit of $20.Write an equation in x to represent this information.
  • Feb 13, 2010, 11:37 AM
    galactus

    Since he paid $500 for all the parafin and paid $x for each liter, then he bought 500/x liters.

    But 3 leaked out and he sold it for $1 more than what he paid.



    Now, you try to do part b. If he made $20 profit, then how much did he gross? Set the expression equal to that and solve for x.
  • Feb 14, 2010, 12:27 AM
    HuiLi

    I think I get something wrong here...
    The equation I get:
    523xsquare+23x-500=0
    The answer:
    3xsquare+23x-500=0

    I can't find the problem with it
  • Feb 14, 2010, 04:57 AM
    galactus

    You made a mistake then. What I showed you reduces to

    Just expand



    and multiply by -x.

    Post how you came up with what you have and maybe we can help. As is, we have no way of knowing how you got that.
  • Feb 14, 2010, 08:52 PM
    HuiLi
    Here is how I get it:

    (x+1)(500/x-3)=520

    (500-3x(x+1)/xsquare+x)-520=0

    500x+500-3xsquare-3x/xsquare+x

    (497x+500-3xsqiare/xsquare+x)-520=0

    (497x+500-3xsqiare/xsquare+x)-(520xsquare+520x)/xsquare+x

    both sides times -x

    23x-500+523xsquare/-xsquare-x =0

    How do I make it an equation from here on?
  • Feb 17, 2010, 04:19 AM
    HuiLi

    (520/x-3)(x-1)

    520=(500x+500/xsquare+x)-3x+3

    520square+520x=500x+500-3x+3

    520xsquare+520x-503x+497=0

    520xsquare+17x+497=0

    this is the new method I can think of,but I still cannto get the answer?is anyone here?
  • Feb 17, 2010, 07:28 AM
    Unknown008

    I think you have got a little problem in expansion:



    I'll take only the left hand side for now.



    Now, I put back the 520 from before:

  • Feb 19, 2010, 05:09 AM
    HuiLi

    Thanks!that is very clear & helpful!
    I finally understand maths & what I did wrong!yay for me :D
  • Feb 19, 2010, 07:34 AM
    Unknown008

    You're welcome :)

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