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Solve for P

  1. Mar 12, 2008 #1
    Solve for P:

    [tex] \frac{p - 10}{-5}=\frac{p - 1}{4}[/tex]


    The most effective way i will learn this embarrassingly simple problem is if you post the solution and i will easily be able to examine it.

    thank you in advance
     
    Last edited: Mar 12, 2008
  2. jcsd
  3. Mar 12, 2008 #2
    is the answer 6 1/3?
     
  4. Mar 12, 2008 #3
    show your steps, don't be embarassed.
     
  5. Mar 12, 2008 #4
    [tex]
    \frac{p - 10}{-5}=\frac{p - 1}{4}
    [/tex]

    [tex]
    p - 5 =\frac{p - 1}{4}
    [/tex]


    [tex]
    4p - 20 = p - 1
    [/tex]

    [tex]
    3p -19 = 0
    [/tex]

    [tex]
    3p = 19
    [/tex]

    [tex]
    p = 19 / 3
    [/tex]


    p = 6 1/3
     
  6. Mar 12, 2008 #5

    cristo

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    Staff Emeritus
    Science Advisor

    Your first line isn't right: what happened to the -5 in the denominator of the left hand side? To start with, I would multiply both sides up by the respective denominators, so you are left with 4(p-10)=-5(p-1). Can you go from here?
     
  7. Mar 12, 2008 #6

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    No, it is not. The most effective way to learn anything is by doing it. Many students fool themselves into looking at a solution by someone else and saying "yes, I understand that now"- but then not being able to repeat even the solution to that problem later much less a different problem of the same sort. What have you tried?

    Personally, I hate fractions. What could I do to get rid of the denominators?
     
  8. Mar 12, 2008 #7
    4(p-10) = -5(p-1)

    4p-40 = -5p+5

    4p+5p = 5+40

    9p = 45

    p = 45/9

    = 5

    is this correct?
     
  9. Mar 12, 2008 #8
    Plug that value into your original problem and see if the left equals the right.
     
  10. Mar 12, 2008 #9
    yes thank you
     
  11. Mar 13, 2008 #10
    I just wanted to jump in and explain something here. The reason your left side operation is illegal is this: You can only do shortening on complete expressions. "+" and "-" divides expressions into parts. So, "A" is an expression, so is "4A" or "4 * 8 * 9". While "A + 1" is in fact two different expressions combined, and so is "4A - 2B" or "4 * 8 + 9".

    You can shorten these:
    [tex]
    \frac{a * b}{b} = a
    [/tex]

    [tex]
    \frac{10 * 5}{5} = 10
    [/tex]

    But not these:
    [tex]
    \frac{a + b}{b}
    [/tex]

    [tex]
    \frac{10 + 5}{5}
    [/tex]

    If you want to shorten a combined expression, you need to shorten the entire thing. You can put parentheses around it and call the whole thing a single expression: (A + 1) is an expression, but to shorten it you need an (A + 1) expression in the denominator as well.

    So, you CAN shorten this:
    [tex]
    \frac{a + b}{3(a + b)} = \frac{1}{3}
    [/tex]

    Shortening works because a fraction is really a division, and a*b divided by b equals a. If you multiply by something, and then divide by the same, you get the original amount. So you simply remove multiples and divides of the same nomination.

    There is a deeper understanding obtainable here, this whole thing is based on certain laws of multiples (like, the order doesn't matter: A * B = B * A) and divisions, which you can look into if so inclined. I assure you, if you start with those laws and build your way up to the fractions, everything will be much clearer. It takes more time, but it is easier than memorizing rules, in a way.

    Caveat emptor: English is a second language to me, so some of the terms I use might not be appropriate. "Expression" might in fact be "Factors" or some such.

    k
     
    Last edited: Mar 14, 2008
  12. Mar 13, 2008 #11
    thanks kenewbie, that gives me something to experiment with. Also, I find that playing around with these rules and just experimenting with concepts in general is making Algebra more and more natural to me ;)
     
  13. Mar 13, 2008 #12

    u might of misunderstood what i meant.. what i meant was: "just post the solution (as i will understand it without additional commentary) and so i can get on with applying it to similar examples " :)
     
  14. Mar 13, 2008 #13
    You misunderstand what Halls is saying. I tutor a lot of people for Algebra, and they always ask me to work a problem. After working it, they are like omg wow that makes so a lot sense ... I ask them to WORK THE SAMEEE PROBLEM, they can't do it. So I would listen to what Halls is saying. Be aware of what you are doing, Math is too important to brush off.
     
  15. Mar 13, 2008 #14


    Thread after thread after thread im getting the same thoughtless comments.

    I do take math seriously. My degree is based on math. Im a 20 year old second year Applied Finance / App Statistics student at top 8 Australian uni, apart form this algebra am currently undertaking I am also currently taking calculus, statistical modelling (in matlab), acounting and economics. As mentioned, im SECOND year and i have ALREADY achieved above average outcomes in my first year.

    I am just here to bridge some serious gaps in my algebra knowledge that i have forgotten since last completing a pure math course 3 years ago at high school. Is that sooo hard to believe. I have already PROVEN learning outcomes at university including several math (finance) units from my first year.

    What’s the point of this boring rant u might be wondering? Well.. it seems u have ASSUMED that im some lazy 6th grade student in elementary school trying to get some one else to do my homework so I can go play some video games.

    Its true and you know it.

    So everytime i ask a question someone manages to throw in some pointless distractions instead of just posting MATH


    You see, when ever I post a math (finance) questions here:

    www.wilmott.com

    or when I post my C++ questions here:

    www.mql4.com


    I ALWAYS get ANSWERS instead of tips on how to study effectively or some other retarded comment.

    Thank you to kenewbie and cristo for actually posting some math.

    besides the help by the people mentioned above, I feel like im in a special ed class here.

    so maybe im on the wrong forum?.. and yes, its rhetorical.

    please ban my account, i dont care .
     
    Last edited: Mar 14, 2008
  16. Mar 13, 2008 #15
    The philosophy here is that if you show work people, can help you by pointing out flaws. Posting answers by other members is discouraged because overall people tend not to learn this way. It's like reading a proof, you might understand it as you read it, but could you reproduce the desired result? Probably not the first time around. If you however could derive that proof, you'd not only know it, but know the underlying concepts that it represents.

    That said no one is going to ban your account. I think you've got a misunderstanding. When someone asks to see your work it is merely to see where you are in the process of finding a solution. Without some work ('even 'I have no clue where to start' helps) the people who are actively posting advice here do not know where to begin.

    EDIT: Also verbal math skills are important to have as well. Being able to understand hints constructed in sentences as opposed to equations is a good skill to have.
     
    Last edited: Mar 13, 2008
  17. Mar 13, 2008 #16
    isnt that obvious? u should trust the student to do the responsible thing and look for the concepts in the solution first. Especially when the question is of such horrid simplicity.

    instead all i got was more questions as if its an interactive-learning-special-ed-class.

    and theres nothing inherently wrong with that, but its painful and degrading when im in the middle if a bachelor's degree.

    well i guess its no-ones fault but my own. I have nothing against PF's teaching philosophy, like i said, im on the wrong forum.
     
  18. Mar 13, 2008 #17
    wait it is just me being tired or that is wrong. Shouldn't it be 1/3 not 1/2(a+b). maybe i didn't real before it.
     
  19. Mar 13, 2008 #18
    Well no offense but it was a pretty basic question. :uhh:

    Questions like these are usually asked by younger people, so I guess people just assumed that you were younger, and that's why it sounded like they were preaching to a "special ed" class, that would be my guess. But you make a good point I think a lot of people are guilty of that.
     
    Last edited: Mar 13, 2008
  20. Mar 14, 2008 #19


    exactly. so as a hint, i said 'just write the solution' in post #1

    and look at the remarks i got in return.
     
    Last edited: Mar 14, 2008
  21. Mar 14, 2008 #20
    Aye, you are of course correct. Can I blame the flex? It is the popular way out :)

    k
     
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