Results 1 to 3 of 3

Math Help - Transposing a fraction with the same unknown

  1. #1
    Newbie
    Joined
    May 2009
    Posts
    5

    Transposing a fraction with the same unknown

    I am struggling to transpose my OWN formula, my math skills are terrible. I have:
    1.5=(x+10)/(x+5)

    I know x is 5 because I made this problem. How do I reverse it and make x the subject?

    I've been trying to work with the PIN example which generally makes sense:
    P=I/N
    I=P*N
    N=N*I is this right?

    What is the best way to remember this? How do you think about this in your head? Why are percentages so easy but this seems to confuse the hell out of me?

    Sam
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Grandad's Avatar
    Joined
    Dec 2008
    From
    South Coast of England
    Posts
    2,570
    Thanks
    1
    Hello Unmath Sam
    Quote Originally Posted by Unmath Sam View Post
    I am struggling to transpose my OWN formula, my math skills are terrible. I have:
    1.5=(x+10)/(x+5)

    I know x is 5 because I made this problem. How do I reverse it and make x the subject?

    I've been trying to work with the PIN example which generally makes sense:
    P=I/N
    I=P*N
    N=N*I is this right?

    What is the best way to remember this? How do you think about this in your head? Why are percentages so easy but this seems to confuse the hell out of me?

    Sam
    You want to solve the equation
    1.5=\frac{x+10}{x+5}
    First, get rid of fractions, by multiplying both sides of the equation by (x+5):
    \Rightarrow 1.5(x+5) = x+10
    Next, remove brackets:
    \Rightarrow 1.5x+7.5=x+10
    Collect x's on one side; everything else on the other:
    \Rightarrow 1.5x-x=10-7.5
    Simplify:
    \Rightarrow 0.5x = 2.5
    Divide to complete the solution:
    \Rightarrow x = \frac{2.5}{0.5}=5
    As far as your other questions are concerned, I'll just correct one of your equations:
    P = \frac{I}{N}

    \Rightarrow I=PN (You got this line correct)

    \Rightarrow N = \frac{I}{P} (I think this is what you meant here)
    Grandad
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member rowe's Avatar
    Joined
    Jul 2009
    Posts
    89

    Slightly different approach

    Here's a slightly different approach.

    1.5 = \tfrac{3}{2}

    \frac{3}{2} = \frac{x+10}{x+5}

    Multiplying both sides by (x+5):

    \frac{3x+15}{2} = x+10

    \frac{3x+15}{2}-x = 10

    \frac{3x+15-2x}{2} = 10

    \frac{x+15}{2} = 10

    x+15 = 20

    x = 5
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: January 15th 2012, 11:57 AM
  2. Transposing Matrices
    Posted in the Advanced Algebra Forum
    Replies: 3
    Last Post: May 15th 2011, 02:07 AM
  3. Transposing of formulae
    Posted in the Algebra Forum
    Replies: 2
    Last Post: October 26th 2009, 03:00 PM
  4. help with transposing
    Posted in the Pre-Calculus Forum
    Replies: 6
    Last Post: November 11th 2008, 05:26 AM
  5. fraction with unknown
    Posted in the Algebra Forum
    Replies: 3
    Last Post: November 5th 2007, 04:57 PM

Search Tags


/mathhelpforum @mathhelpforum