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Math Tips & Tricks

Discussion in 'General Discussions' started by WeRAnonymous, Sep 9, 2011.

  1. Today, I learned a really cool trick for multiplying numbers by 11. I'll explain it best I can. But it's a lot easier to explain when you have voice and words.

    First, you take the number (that is not 11) and put a space between the digits.
    Second, add the digits together and put that number in the newly made space.
    If the digits add-up to a two digit number, you add the frist digit of it to the first digit of the other number.
    Now seems like a good time for an example.

    18X11 - 1_8 - 198

    58X11 - 5_8 - (5+1)38 = 638

    As far as I know, this only works if you are multiplying 11 by a two digit number.

    I hope that was clear. And, now, the reasons I am posting this. Frist, I thought this was really cool. A little disappointed I'm just now learning it.

    Second, I was wanted to know if you know any cool math tips or tricks you wanna share with a less savvy mathematician.
     
  2. Zweiblumen

    Zweiblumen Slightly Tilted

    Location:
    Iceland
    A children's trick for calculating 1 to 9 x 9. Hold up your hands (assumes 10 digits/fingers). Now bend the finger that represents the number to multiply.
    The number of fingers in front and behind the bent finger are the answer. Ie. 3x9 => 2 fingers, bent finger, 7 fingers = 27.
    This works because the sum of the digits in the answer are always 9 .
     
  3. Cayvmann

    Cayvmann Very Tilted

    On the radio this morning the geniuses that host the morning show told of a math trick that wowed them to death. If you add your birth year to the age you will be this year, you will get 2011. Wow, I know, right?

    How do people like this even tie their shoes, and get out of bed in the morning, to get to work?
     
  4. wow. that's kinda cool.

    I'm not sure how they function, but I'd say they have more than enough time on their hands. But it works.

    I learned another one today, for dividing numbers by 9, 99, and 999. Any number divided by 9 (99 or 999) just repeats itself, over and over.

    so 5/9 = .555555555
    and 17/99 = .17171717171717
    and 153/999 = .153153153153153
     
  5. the_jazz

    the_jazz Accused old lady puncher

    Only if the number is smaller than divisor. So:

    27/9 = 3
    25/9 = 2.77777777
    100/99= 1.01010101
     
  6. streak_56

    streak_56 I'm doing something, going somewhere...

    Location:
    C eh N eh D eh....
    ah math.... my first love....

    never go to Alabama to learn pi..... that my tip... and yes.... I realize it was a hoax.....

    I don't like using a calculator for most of my math because I feel it keeps me on edge. There's other ones, such as if you add all the digits of a multiple of nine, they will equal nine.... hence 27= 2+7= 9, 117=1+1+7=9.
     
  7. Yeah, I saw that while I was playing with it. Tried to remind myself to say something about it - looks like I still forgot, so thanks for bringing it up. :)

    Yeah, Jazz, that was pretty much the only math trick I knew until recently.
     
  8. I haven't learned any new math tricks ... And I guess neither has anyone else ...
     
  9. When multiplying larger numbers by 5, I find it easier to divide by 2, then move the decimal point one place to the right (or, multiply by 10).

    852/2=426, 426x10=4260

    It may seem like you're adding a step, but I find it quicker to calculate in my head than 5x2, carry the 1, (5x5)+1, carry the 2....

    Oh, dd3953! Please bump your font at least one size... these old eyes of mine are really straining, even with my bifocals! Thanks!
     
    • Like Like x 1
  10. Fremen

    Fremen Allright, who stole my mustache?

    Location:
    E. Texas
    I got a tip for you. Get an accountant and some leverage on him/her to keep 'em honest.
     
  11. greywolf

    greywolf Slightly Tilted

    7 is one of my favourite numbers because to work out fractions you only need to know one set of recurring numbers - .142857. All fractions of seven have this same recurring pattern, and you only need to move the decimal around:

    1/7 = 0.142857...
    2/7 = 0.2857142857...
    3/7 = 0.42857142857...
    4/7 = 0.57142857...
    5/7 = 0.7142857....
    6/7 = 0.857142857

    The trick for multiplying by nine by a single digit is subtract 1 from the single digit and add whatever is required to make the individual digits add to 9:

    1 x 9 = 0 + (9-0) = 9
    2 x 9 = 1 + (9-1) = 18
    3 x 9 = 2 + (9-2) = 27
    etc.
     
  12. Up one, I can do. Hope that's better. Yeah, I think I like that one, gonna have to spend some time playing with it to be sure.

    Oh, if only it was that easy! :)

    So, how do you know where the .142857 starts? Or what comes before it?

    This one, I think I can get my head around, and maybe remember.
     
  13. greywolf

    greywolf Slightly Tilted

    You do have to figure out where to start, but with 0.14... for 1/7th, you can usually figure out which number to start with for any other value. You just have to remember the "142857" pattern; once you hit the "1" in your decimal, it just continues as "142857" over and over through to infinity.

    And Fremen... I'm an accountant! I resent your insinuation. I don't deny it, I just resent it! ;)
     
    • Like Like x 1
  14. Bodkin van Horn

    Bodkin van Horn One of the Four Horsewomyn of the Fempocalypse

    Always double check your work. It will save you headaches later on.
     
  15. RogueGypsy

    RogueGypsy Vertical

    A slightly easier way to multiply 9 for single digits is to remember, as mentioned above, that the sum of the digits when added always equals 9. Knowing that, it's easy to chart the answers ascending or descending from 1-10.

    09
    18
    27
    36
    45
    54
    63
    72
    81
    90

    Note the ten's column is ascending from 0-9 and the ones column is descending from 9-0.
     
  16. Remixer

    Remixer Middle Eastern Doofus

    Location:
    Frankfurt, Germany
    Since we have maths fanatics here, I'll try your help!

    Does anyone know how to do synthetic division? I mastered factoring, cartesian graphing and long division of polynomials, but the process of synthetic division fucks my brain. Maybe it's that huge line, or the reversal of the groupings, I don't know.

    Polynomials with a degree higher than 6 are especially hard for me.

    Let's say, employ synthetic division for:

    (3x^4 - 5x^3 + 8x^2 - 2x + 4) / (x^2 - 7)

    How would you go about it? Figure out the remainder first? Or calculate the zeroes? Or simplify? Or ...?
     
  17. Remixer

    Remixer Middle Eastern Doofus

    Location:
    Frankfurt, Germany
    Nobody?

    ...

    *sulks*
     
  18. Wow. It's been such a long time since I've logged in.

    I just learned how to synthetic division. It's really cool.

    But I'm not really sure what you are asking. You could simplify before you divide. ...