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Math Help - Can't do this basic problem!

  1. #1
    Member Awsom Guy's Avatar
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    Can't do this basic problem!

    I cannot do this problem.
    Question:
    0.7 = s/335 - s/5300
    Find s.

    do I do it as a quadratic or how else.
    Thanks for help.
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  2. #2
    Super Member Bacterius's Avatar
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    Hello,
    just substract the two fractions by taking the greatest common divisor of 335 and 5300. Then you are left with a linear equation.
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  3. #3
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    Quote Originally Posted by Awsom Guy View Post
    I cannot do this problem.
    Question:
    0.7 = s/335 - s/5300
    Find s.

    do I do it as a quadratic or how else.
    Thanks for help.
    Or....

    just multiply both sides by 335 and then multiply both sides by 5300
    as the sides will remain equal.

    0.7=\frac{s}{335}-\frac{s}{5300}

    0.7(335)=s-\frac{335s}{5300}

    0.7(335)(5300)=5300s-335s=4965s

    1242850=4965s

    s=\frac{1242850}{4965}
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  4. #4
    Member Awsom Guy's Avatar
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    Wait.
    The second step where you moved just multiplied both sides doesn't make any sense. Shouldn't you make fraction. Doing it that way I got the answer 444447165.16
    Is that right or is Archie right.
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  5. #5
    Super Member Bacterius's Avatar
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    0.7=\frac{s}{335}-\frac{s}{5300}

    0.7=\frac{5300 \times s}{335 \times 5300}-\frac{335 \times s}{5300 \times 335}

    0.7=\frac{5300 \times s - 335 \times s}{335 \times 5300}

    0.7=\frac{s(5300 - 335)}{335 \times 5300}

    0.7=\frac{4965s}{1775500}

    0.7 \times 1775500=4965s

    \frac{0.7 \times 1775500}{4965}=s

    s \approx 250.322

    Does it make sense now ?
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  6. #6
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    Quote Originally Posted by Awsom Guy View Post
    Wait.
    The second step where you moved just multiplied both sides doesn't make any sense. Shouldn't you make fraction. Doing it that way I got the answer 444447165.16
    Is that right or is Archie right.
    If you have

    \frac{3}{5}-\frac{2}{5}=x

    then you can just multiply both sides by 5 to get 3-2=5x

    It's the same as combining the fractions to get \frac{3-2}{5}=x

    You can either combine the fractions or just multiply both sides by the denominators.

    x=\frac{1}{2}+\frac{1}{3}=\frac{3}{6}+\frac{2}{6}=  \frac{5}{6}

    2x=1+\frac{2}{3}

    6x=3+2=5

    is another way.

    If x=5, then 2x=10 by multiplying both sides by 2, they are still equal and saying the same thing.

    5=5, 5(2)=5(2), (3+2)=5, 2(3+2)=2(5)

    If two sides are the same, then if you multiply all terms of both sides
    by the same number, they will still be equal.

    You should get used to adding fractions, so that it becomes easy,
    however, multiplying by the denominators in this case is faster.
    Last edited by Archie Meade; May 18th 2010 at 11:19 AM. Reason: small but significant typo
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  7. #7
    Member Awsom Guy's Avatar
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    WOW great explanation, sorry I have trouble with the basics.
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  8. #8
    Member Awsom Guy's Avatar
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    So Bacterius if I multiply one side by 335 I don't have to multiply other side by 335. Correct.
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  9. #9
    Super Member Bacterius's Avatar
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    Quote Originally Posted by Awsom Guy View Post
    So Bacterius if I multiply one side by 335 I don't have to multiply other side by 335. Correct.
    Consider \frac{3}{5}. This is the same as \frac{3 \times 7}{5 \times 7} (since the seven cancels out). This trick allows us to set two different fractions to the same denominator, in order to add them easily.

    Note : you are not actually doing anything to the equation by multiplying by 335 inside the fraction : you are only rewriting a fraction in a different form (but it is equivalent) to make it simpler to add. Therefore, since the equation is left unchanged, doing anything to the other side would be superfluous. Simple example :

    \frac{3 \times 7}{5 \times 7} = \frac{3}{5} \times \frac{7}{7} = \frac{3}{5} \times 1 = \frac{3}{5}

    See ? It is basically equivalent to multiplying the fraction by 1, but adding multiplicative information to allow fraction addition. Since multiplying by 1 does not change anything, there is nothing to change on the other side of the equation
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  10. #10
    Member Awsom Guy's Avatar
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    Thanks Ray.
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