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Algebra with fractions

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    I have to find out what n equals for the equation below:
    \frac{1}{2n}+\frac{1}{3n}=7
    I'm confused on how I start off. This is mainly because of n being the the denominator. :confused:
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    Think about what would happen if you were to multiply both sides by something?
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    Do you mean by 6n as it's the LCM of 3n and 2n? or by just 6?
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    (Original post by krisshP)
    I have to find out what n equals for the equation below:
    \frac{1}{2n}+\frac{1}{3n}=7
    I'm confused on how I start off. This is mainly because of n being the the denominator. :confused:
    You need to put it all over a common denominator e.g. 6n like you suggested it can't just be six a 'n' is also a common factor between the two. LCM is exactly right
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    (Original post by books28)
    You need to put it all over a common denominator e.g. 6n like you suggested it can't just be six a 'n' is also a common factor between the two. LCM is exactly right
    Okay. I understand why I have to make 6n be the denominator. But how do I do that. The fact that the 2n and 3n are the denominators puts me off and makes it all hard for me.
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    \frac{1}{2n}=\frac{3}{6n}

    Does that help?
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    Sophie's suggestion is easier by the way!
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    I think I worked it out but I'm not sure:
    \frac{1}{2n}+\frac{1}{3n}=7
    I multiply both sides by 3n, giving the following:
    \frac{3n}{2n}+1=21n
    I minus 1 from both sides to give the following:
    \frac{3n}{2n}=21n-1
    the Ns on the faction cancel out to give:
    \frac{3}{2}=21n-1
    This causes in a different form:
    1.5=21n-1
    Adding 1 to both sides provides:
    2.5=21n
    Then dividing both sides by 21 to get n on its own gives:
    0.119047619047619047619047619047  62 = n

    Is this a right method or not?
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    1/2n+1/3n=7
    1/2*1/n+1/3*1/n=7
    (1/2+1/3)*1/n=7
    You finish it off.
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    (Original post by krisshP)
    Then dividing both sides by 21 to get n on its own gives:
    0.119047619047619047619047619047  62 = n

    Is this a right method or not?
    Yes but horribly long winded. Can you use fractions rather than decimals?

    Easier would be just to multiply by 6n.
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    so answer is 2.5/21
    Thanks!
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    (Original post by krisshP)
    so answer is 2.5/21
    Thanks!
    Have you ever seen a fraction that looks like that?
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    (Original post by krisshP)
    so answer is 2.5/21
    Thanks!
    It's 5/42.
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    I know. sorry. My clumsy mistake

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Updated: April 15, 2012
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