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Math Help - Algebra question?

  1. #1
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    Algebra question?

    Hello,

    In attachment I show an algebraic equation which needs to solve for "v". V is supposed to have a result of 4.09, but I get 35??

    Can someone please show me where I went wrong!

    Thank you in advance
    Attached Thumbnails Attached Thumbnails Algebra question?-math.jpg  
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  2. #2
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    Re: Algebra question?

    3(v+5)+6(v-10)+2v=0
    3v+15+6v-60+2v=0
    11v-45=0
    11v=45
    v=45/11
    v=4.09

    U need to use the smaller denominator(600).then u will not get confuse.
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  3. #3
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    Re: Algebra question?

    The first thing edwintan did was multiply both sides by the "least common multiple" of the three denominators, 600. That immediately gets rid of all fractions.
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  4. #4
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    Re: Algebra question?

    Edwintan,

    can you please explain what value you multiplied each term
    to get the first line. for example how did you get
    3(v+5) from v+5/200 ???

    did you multiply each term like this:
    = 600/1 * v+5/200
    = 3(v+5)
    ??
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  5. #5
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    Re: Algebra question?

    The first thing edwintan did was multiply both sides by the "least common multiple" of the three denominators, 600. That immediately gets rid of all fractions.
    yes, okay that's one way, but why can't I
    take the lowest common denominator of the three
    which is 600 and use it as a divider like this:

    a) 200 goes into 600 3 times... so multiply first
    term by 3/3
    b) 100 goes into 600 6 times... so multiply 2nd
    term by 6/6
    c) 300 goes into 600 2 times... so multiply 3rd
    item by 2/2

    this should be legal as we do the same for this:

    1/2 + 2/3

    so,
    lowest common den= 6

    2 goes into 6 3 times so mul by 3/3
    and 3 goes into 6 2 times so mul by 2/2

    therefore:
    (3/3 x 1/2) + (2/2 x 2/3)

    becomes:
    3/6 + 4/6 = 7/6

    why can't we do this with the 600 in my initial example???
    Last edited by simplyComplex; October 30th 2012 at 02:46 PM.
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  6. #6
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    Re: Algebra question?

    Your example is using 60000 .U can use 60000 and try it. U will still get the same answer. But if u use a larger figure , mistakes are sure to happen.
    So If can sure a small figure less mistake is possible.
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  7. #7
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    Re: Algebra question?

    Your example is using 60000 .U can use 60000 and try it. U will still get the same answer.
    no you won't!

    using 60000 as a common denominator:

    a) 200 goes into 600 3 times... so multiply first term by 300/300
    b) 100 goes into 600 6 times... so multiply 2nd term by 600/600
    c) 300 goes into 600 2 times... so multiply 3rd item by 200/200

    (300/300) x (v+5/200) + (600/600) x (v-10/100) + (200/200) (v/300) = 0
    300(v+5/200)/60000 + 600(v-10/100)/60000 + 200v/60000 = 0
    (300v + 1500 + 600v - 6000 + 200v) / 60000 = 0
    (1100v +1500 - 6000) / 60000 = 0
    (1100v - 4500) = 60000
    1100v = 60000 + 4500
    v = 64500/1100
    v = 58.6 ???



    *** BUT ***

    why is it the using the same analogy as above it works for a similar equation like this:

    1/2 + 2/3

    lowest common denominator= 6

    a) 2 goes into 6 3 times so multiply 1st term by 3/3
    b) 3 goes into 6 2 times so multiply 2nd term by 2/2

    therefore doing the exact same reasoning as the equation above we do:
    (3/3 x 1/2) + (2/2 x 2/3)

    becomes:
    3/6 + 4/6 = 7/6

    and why here it works and above it doesn't??
    someone... anyone please...

    thanks
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  8. #8
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    Re: Algebra question?

    (300/300) x (v+5/200) + (600/600) x (v-10/100) + (200/200) (v/300) = 0
    300(v+5/200)/60000 + 600(v-10/100)/60000 + 200v/60000 = 0
    (300v + 1500 + 600v - 6000 + 200v) / 60000 = 0
    (1100v +1500 - 6000) / 60000 = 0
    (1100v - 4500) = 60000
    1100v = 60000 + 4500
    v = 64500/1100
    v = 58.6 ???

    As per above u are using the wrong method .see below for the correction..
    (1100v +1500 - 6000) / 60000 = 0

    1100v-4500/60000=0/1

    60000/60000 x (1100v-4500)=60000/1 x 0

    therefore it become 1100v - 4500 = 0

    1100v = 4500

    v=4500/1100

    v=45/11 = 4.09

    Some of your working method is wrong..
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  9. #9
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    Re: Algebra question?

    oh I see what's going on...

    Thanks for your help edwintan!

    sc
    Last edited by simplyComplex; November 1st 2012 at 06:36 PM.
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  10. #10
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    Re: Algebra question?

    isn't the symbol u used on the right of the equal sign the symbol for golden ratio?

    Besides the point ,u can't just multiply 600/300 and 600/200 with the fractions just to get the denominators even, 'cause u would change the fraction entirely. its just like multiplying by 2 and 3, respectively.

    However, multiplying to get common denominators of 60000 to solve for v works just as well:


    [(v+5)/200]*(300/300) + [(v-10)/100]*(600/600) + [v/300]*(200/200) = 0
    { (v+5)/200]*(600/300) + [(v-10)/100]*(600/600) + [v/300]*(600/200) DOESNOT= 0 }
    (300v+1500)/60000 + (600v-6000)/60000 + 200v/60000 = 0
    300v+1500+600v-6000+200v = 0
    1100v-4500 = 0
    1100v = 4500
    11v = 45
    v = 45/11 = 4.09
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  11. #11
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    Re: Algebra question?

    thanks very much for your help guys!
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