Results 1 to 4 of 4

Math Help - Missing Basic Algebar Rules

  1. #1
    Newbie
    Joined
    Mar 2007
    Posts
    11

    Missing Basic Algebar Rules

    Since I've been in Accounting & Finance classes, I've realized I must have missed a lot in Algebra back in the day.

    Let me give you an example (it's Finance, but needs Algebra)...

    Say you have:

    Return on Assets = Net Income / Total Assets

    You've been given:

    6% = Net Income / $90

    Ok, so to find net income you take .06 X $90. Why?

    The idea is to get Net Income by itself? Other problems seem to use division instead of multiplication after you get the 'missing' portion by itself.

    Does this make any sense?? Know what I mean?

    When would you divide instead of multiply? (Probably an extremely thick question) but is the denominator always on the bottom no matter what case if you're dividing or rearranging a problem in this manner?

    Thanks for any help.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by matius View Post
    Since I've been in Accounting & Finance classes, I've realized I must have missed a lot in Algebra back in the day.

    Let me give you an example (it's Finance, but needs Algebra)...

    Say you have:

    Return on Assets = Net Income / Total Assets

    You've been given:

    6% = Net Income / $90

    Ok, so to find net income you take .06 X $90. Why?

    The idea is to get Net Income by itself? Other problems seem to use division instead of multiplication after you get the 'missing' portion by itself.

    Does this make any sense?? Know what I mean?

    When would you divide instead of multiply? (Probably an extremely thick question) but is the denominator always on the bottom no matter what case if you're dividing or rearranging a problem in this manner?

    Thanks for any help.
    ok, first of all i asume you know why 6% = 0.06, ok, let me not assume anything.

    "Percentage" is a fancy word for "/100" or "out of 100," so basically a percentage is a fraction where the denominator is 100

    so 25% = 25/100 = 0.25, 5% = 5/100 = 0.05, 6% = 6/100 = 0.06 etc.

    Now, what you are asking about is solving an equation. Basically you have an expression with an equal sign, where one thing is unknown, and your objective is to get that unknown on one side of the equal sign by itself. basically, if there is anything else with the unknown on the same side, you do the opposite operation that thing is doing. since there is an equal sign, you have to maintain the equality by doing the same thing on the other side.

    example:

    5 = x + 2
    we want to get x on one side by itself, but there is a +2 beside it, so we do the opposite operation, that is, we minus 2. however, to maintain the equality, we have to minus 2 from the other side as well. so we get:

    5 - 2 = x + 2 - 2
    5 - 2 = x
    3 = x
    therefore, x = 3

    a similar concept applies when multiplying and dividing.

    25 = x/5
    we want x on one side, but there is a 5 dividing it, so we do the oppostie, we multiply by 5, so that will cancel out the 5 that is there. since it is an equation, we must do the same thing on the other side. so,

    25 * 5 = x/5 * 5
    5 = x
    therefore, x = 5

    what if the x was on the bottom of the fraction, well, there are two typical ways to deal with that.

    5 = 25/x
    ok, we can follow the same principle we have been using the whole time. since we have a 25 on top, we can divide by 25, or multiply by 1/25, that is where 25 is on the bottom to cancel the one on top. but be careful, when doing this we don't end up with x on one side, we end up with 1/x

    5/25 = 25/x /25
    5/25 = 25/x * 1/25
    5/25 = 1/x
    now flip both sides
    25/5 = x
    therefore, x = 5

    or, we could move the x first.

    5 = 25/x ..........multiply by x on both sides
    5 * x = 25/x * x
    5x = 25 .......now we have a 5 times x, so do the opposite, divide by 5
    5x / 5 = 25/5
    x = 5

    another method is we can cross multiply. that is, we take the denominator of one side times the numerator of the other side, and put that answer on one side of the equal sign, then do the same thing with the numerator and denominator on the opposite side.

    5 = 25/x
    5/1 = 25/x
    5*x = 1*25
    x = 25/5
    x = 5

    so there are general patterns here, that you get familiar with the more you do them. if you do enough problems, you will be able to do these automatically without even thinking of the rules.

    Let's say in all the following, we want to solve for a. i will try to put a in every possible position you may come across it in.

    a + b = c
    => a = c - b

    a - b = c
    => a = c + b

    a/b = c/d
    => a = b*c/d

    b/a = c/d
    => a = b*d/c

    and we can mix these up:
    example

    a/b + c = d
    a/b = d - c
    a = b*(d - c)

    you can try some others.

    So now to do your problem:

    6% = Net Income / $90

    => 0.06 = NetIncome/90 .......we have 90 dividing, so multiply by it on both sides
    => 0.06 * 90 = NetIncome/90 * 90
    => 5.4 = NetIncome

    Try to grab an algebra book and practice some of these problems, or practice a lot of them in your finance text book, come back here with your solutions and we'll tell you your mistakes...if you make any
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Mar 2007
    Posts
    11
    Can't tell you how much that helps me. Thank you!

    It's very clear to me how this works now, but you're right, will need to practice before it really sets in.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by matius View Post
    Can't tell you how much that helps me. Thank you!
    good! glad to be of service

    It's very clear to me how this works now, but you're right, will need to practice before it really sets in.
    yes, practice is necessary, even for people who are good with math (unless you're Guass reincarnated). you can always come back here to check the work that you have done
    Last edited by Jhevon; April 22nd 2007 at 09:06 AM.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 3
    Last Post: May 27th 2011, 01:53 PM
  2. Basic Matlab help. Can't seem to grasp basic concept
    Posted in the Math Software Forum
    Replies: 5
    Last Post: February 28th 2010, 09:12 PM
  3. I'm missing something
    Posted in the Statistics Forum
    Replies: 7
    Last Post: January 28th 2010, 06:45 AM
  4. I have a basic principle missing
    Posted in the Calculus Forum
    Replies: 1
    Last Post: November 29th 2009, 08:59 AM
  5. Replies: 6
    Last Post: November 6th 2009, 10:28 PM

Search Tags


/mathhelpforum @mathhelpforum