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Math Help - Here's another question on finding X

  1. #1
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    Here's another question on finding X

    Is there a trick to finding the value of X?

    Example:
    75% of x = 1050
    90% of x = 1260

    I know that x = 1400, but I'm wondering if there's an easy way to find it out quickly.

    Thx!
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  2. #2
    Behold, the power of SARDINES!
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    Quote Originally Posted by matoau View Post
    Is there a trick to finding the value of X?

    Example:
    75% of x = 1050
    90% of x = 1260

    I know that x = 1400, but I'm wondering if there's an easy way to find it out quickly.

    Thx!
    of = "Multiply" 75 \%=\frac{3}{4} \mbox{ and }90 \%=\frac{9}{10}

    so solving each equation gives.

    \frac{3}{4}x=1050 \iff x=\frac{4}{3}1050=4 \cdot 350=1400

    and the second

    \frac{9}{10}x=1260 \iff x =\frac{10}{9}1260=10 \cdot 140=1400

    Fractions can make calculations alot easier.



    I hope this helps.
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  3. #3
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    Yes Yes Yes!
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  4. #4
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    actually, i'm confused (again) at this part:
    <br />
 x=\frac{4}{3}1050=4 \cdot 350=1400<br />

    how does this give us 4? and why is the 4 and 3 flipped? division?
    <br />
 x=\frac{4}{3}1050=4 <br />

    also, where does this come from?
    <br />
4 \cdot 350<br />


    yeah, so where does the the 350 and 140 come from? how is it derived?
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  5. #5
    Behold, the power of SARDINES!
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    \frac{3}{4}x=1050 so we divide both sides by 3/4

    \frac{\frac{3}{4}x}{\frac{3}{4}}=\frac{1050}{\frac  {3}{4}}

    remember that 1050 can be written as a fraction \frac{1050}{1}

    and if we have a fraction divided by a fraction it is the same as multiplying by the reciprocial.

    So now we get...

    x=\frac{\frac{1050}{1}}{\frac{3}{4}}=\underbrace{\  frac{1050}{1}\cdot \frac{4}{3}}_{1050/3=350}=350 \cdot 4=1400

    I hope this clears it up
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  6. #6
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    Yes, thank you...
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  7. #7
    Senior Member Twig's Avatar
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    hi

    Just divide 1260 with 0,9.

    1260/0.9 = 1400
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  8. #8
    Super Member angel.white's Avatar
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    Quote Originally Posted by Twig View Post
    Just divide 1260 with 0,9.

    1260/0.9 = 1400
    Fractions > Decimals
    Quote Originally Posted by TheEmptySet View Post
    \frac{3}{4}x=1050 so we divide both sides by 3/4

    \frac{\frac{3}{4}x}{\frac{3}{4}}=\frac{1050}{\frac  {3}{4}}

    remember that 1050 can be written as a fraction \frac{1050}{1}

    and if we have a fraction divided by a fraction it is the same as multiplying by the reciprocial.

    So now we get...

    x=\frac{\frac{1050}{1}}{\frac{3}{4}}=\underbrace{\  frac{1050}{1}\cdot \frac{4}{3}}_{1050/3=350}=350 \cdot 4=1400

    I hope this clears it up
    Nice Latex
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