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Math Help - SAT algebra equation

  1. #16
    MHF Contributor Unknown008's Avatar
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    Quote Originally Posted by vaironxxrd View Post
    I see you simplified the fraction So that would be 2*7 and 2*3 -1?
    In fact, it will be 2*7 first, to get a new fraction. Then, you do the other operations.

    Spoiler:


    \dfrac{14}{3} - 1

    Then, you do the subtraction:

    \dfrac{14-3}{3}

    You know how to combine fractions I hope
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  2. #17
    MHF Contributor Unknown008's Avatar
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    Quote Originally Posted by vaironxxrd View Post
    yea it is 1.5 But if you do 2*1.5 you get 3 not 2*1.5-1
    Right, but wrong at the same time.

    With this method, you are first looking for the value of x. When you get that, only then that you find 2x - 1.

    This gives (2*1.5) - 1

    and from there you simplify.
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  3. #18
    A Plied Mathematician
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    Too many cooks spoil the broth, and too many educators spoil the class, at least in my opinion. I'm bowing out of this one.
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  4. #19
    Senior Member vaironxxrd's Avatar
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    Quote Originally Posted by Ackbeet View Post
    No, no. You multiply the scalar 2 times the fraction 7/3. THEN you add the fractions by getting a common denominator.
    Making it 2/1 times 7/3? By the way thanks for all the help
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  5. #20
    Senior Member vaironxxrd's Avatar
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    Quote Originally Posted by Unknown008 View Post
    Right, but wrong at the same time.

    With this method, you are first looking for the value of x. When you get that, only then that you find 2x - 1.

    This gives (2*1.5) - 1

    and from there you simplify.
    So you would get 2*1.5 =3 and then [Math]\dfrac{3}{1}[/tex] Which is the same has 3?
    Last edited by mr fantastic; February 14th 2011 at 11:04 AM. Reason: Fixed latex.
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  6. #21
    MHF Contributor Unknown008's Avatar
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    Quote Originally Posted by vaironxxrd View Post
    Making it 2/1 times 7/3? By the way thanks for all the help
    Right. What does 2/1 times 7/3 give?

    Quote Originally Posted by vaironxxrd View Post
    So you would get 2*1.5 =3 and then [Math]\dfrac{3}{1}[/tex] Which is the same has 3?
    Yes, you get 3 first.

    (2*1.5) - 1

    Working out the brackets gives 3. Then, this results in:

    3 - 1

    Then, you can still simplify.

    Sorry Ackbeet, I was trying to see what method the OP was more familiar about and could use more at ease and overlooked the fact that it is becoming difficult to keep track of everything going on. I won't do it again
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  7. #22
    A Plied Mathematician
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    Quote Originally Posted by Unknown008 View Post
    Sorry Ackbeet, I was trying to see what method the OP was more familiar about and could use more at ease and overlooked the fact that it is becoming difficult to keep track of everything going on. I won't do it again
    Don't be worried. It was quite a cheerful "bowing out" on my part. I'm not angry at anybody.
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  8. #23
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    I completely agree with Ackbeet's assertion about "too many mathematicians..." and I would love to bow out of this as well. But I feel that I should give one more post since I believe that I am the person most qualified to help you here. The advice you are getting is all correct, and great from an educational viewpoint, but it's too overwhelming and will not directly translate into a higher SAT score for you.

    So I am going to restate the original question, repeat my original solution and then give you an algebraic solution.

    The original question should be:

    If 2x+2x+2x=12, then 2x-1=.

    Simple strategy: "Take a guess"

    Try to take a reasonable guess for x. Let's try x=3. Then 2(3) + 2(3) + 2(3) = 6+6+6=18, too big.

    So let's try x=2. Then 2(2)+2(2)+2(2) = 4+4+4=12. Just right.

    So x=2 and 2x-1=2(2)-1=4-1=3.

    Note that you can do all of these computations quickly in your calculator.


    More advanced strategy: "Algebraic solution"

    2x+2x+2x=12

    6x=12

    x=2

    So, type in your calculator 2*2-1 and the answer 3 will pop out.

    Remarks:

    (1) On the SAT you will never have to do any computations with fractions. You can always just use your calculator.

    (2) When taking practice tests, or the actual test, you should always use my first method of "taking a guess." You should only practice the second method after you already know how to get the answer the first way. Practicing the second method is a good way to raise your level of mathematical maturity - this is helpful in the long term, but will not produce short term results.

    (3) These remarks are only for the OP - they are based on his specific PSAT score and are not meant to be followed by everyone.

    (4) I realize that my advice is subjective, but they are based on over 10 years experience as an SAT Math tutor. When it comes to standardized tests sometimes the things you don't teach can be as important as the things you do. As a simple example, sometimes teaching a method that is too advanced will simply cause a student to shut down and stop working on any problems at all.

    Final remark: This post is not meant to be condescending to anyone in any way. I think it's great that so many people are pitching in and helping the OP, and this is in no way meant to discourage that. I only made this post to put some things in perspective and to be as helpful as possible. Having worked with hundreds of students with the same SAT ability level I feel obligated to try to help the OP learn strategies that will be the most useful in raising his score, while keeping him motivated to keep practicing.
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  9. #24
    Junior Member MoniMini's Avatar
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    2x + 2x + 2x + 2x = 12 = 8x = 12

    1x = 12/8 = 1.5

    So 2x = 1.5*2 = 3.0

    So 2x - 1 = 3.0 - 1
    Which is equal to 2.0

    Hope it helped

    ~MoniMini @(^_^)@
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