Ask MetaFilter posts tagged with maths

Help me relearn mathematics and its practica applications

dcbarker — Fri, 01 Aug 2008 05:19:32 -0800

Applied Math Filter: Help me use math! I'd like to learn more about mathematics and it's practical applications - particularly in Computer Science I'm a Computer Networking graduate (under 25) who never really done much math at university. My course was somewhere between computer science and communications engineering so maths sort of slipped through the cracks.

Now, I'm looking to re-learn math. I know that a lot of mathematics is abstract but I'm having difficulties seeing practical applications.

Where I'm at:
I took calculus at high school but just scraped through (I spent more time fighting with the teacher than learning). I don't remember a bit of it. I'm pretty much at "square one" so will be learning from the start. I consider myself a quick learner in most areas but had a horrible foundation in math so never picked it back up. I've bought a couple of math books which should teach me the theory I need. I've always thought graphing calculators were pretty interesting but lack the mathematical knowledge to necessitate their use (or purchase). I'm currently in the process of ditching my "college job" to go for a "real job".

What I want:
I want to learn math with a view to using it practically (preferably in computer science).

How you can help:
I'd like suggestions on how I should go about learning mathematics and its practical applications. Which areas should I look at if I want to use mathematics in computing? I think my problem is that I can't see a practical application for math that I'd like to explore but I have a strong urge to develop my mathematics skills.

Any help would be greatly appreciated! Thanks!

How can I help my (nearly) seven year old son "get" maths?

h00py — Wed, 30 Jul 2008 03:00:14 -0800

How can I help my 6 1/2 year old son to *get* maths? It hasn't clicked with him at all and I find myself getting frustrated with having to repeat really basic stuff when helping him with his homework. I'm not a maths genius myself and I really don't want to put him off by getting cranky because he's just not getting it. How do I help him get it? He's a really very bright little fellow who can read exceptionally well and his vocabulary is excellent. He's good with words. It's numbers that he hasn't come to terms with yet. Reading the clock, money, simple addition (and subtraction); all of these things are not within his frame of reference at the moment. How can I help him get the decimal system? I figure that once he's got the whole 'there's only 9 numbers and zero and then you go up a notch and then another notch and so on' at least he'll have somewhere to work from.

He doesn't have to become a mathematician, I just want him to find a good place to start so it all makes some sense. At the moment, he's baffled.

%

dydecker — Fri, 13 Jun 2008 13:41:08 -0800

I am useless at mathematics. If company A grows at 5% a month, how much bigger is it after one year? Answers in percentage terms

Best way to tile a sphere ?

silence — Mon, 02 Jun 2008 07:07:53 -0800

How can I tile a sphere using the minimum number of differently shaped units? I have a 3 meter diameter sphere and I need to tile it using units that are each about 400 square cm (ie like a 20 x 20cm square). The units must be flat (ie, not spherical triangles). I'm currently thinking of using a geodesic tiling, but a (for instance) a 5V geodesic tiling results in (i think) 6 different tile shapes, and also has the problem that the density of tiles isn't constant over the surface - there are obvious visual artefacts where the tiles bunch up. I need to try to minimise the number of different types of unit, and to optimise the appearance so that it's as even as possible. Are there any better ways of tiling a sphere?

How can I implement an s-curve function in excel?

matholio — Wed, 16 Apr 2008 17:48:00 -0800

How can I implement an s-curve function in excel? I have some programming experience, but my maths is crap.
I want a generic function to use to to effect a smooth transition between two numbers. Asigmoid funtion seem useful.

I have read throught these pages :
http://en.wikipedia.org/wiki/Sigmoid_function
http://www.computing.dcu.ie/~humphrys/Notes/Neural/sigmoid.html

But my poor math skills stop me from implementing it.
I do not understand how to transfer the equations I see in to code, or excel.

Much of the problem is I can't properly read and understand the notation used in math functions.
I did ask in an IRC math channel, but several people laughed.

If someone could show me how to implement the sigmoid function in excel, it would help me learn.

Thanks

Silly question about flashing...

twine42 — Wed, 06 Feb 2008 07:44:13 -0800

I have a question about persistence of vision and flashing lights... There will be maths and biology involved. Imagine you have two LEDs. They each produce one hypthetical unit of light (1 HUL if you will). If they're both turned on, they produce a combined 2HUL.

Now imagine that they flash at a rate greater than 25fps in a way that when one is on the other is off.

Ideally they are producing 1HUL. In reality the light up time probably means it's a little less than this. But here is my question:

What does the human eye *think* they are producing? Do you see the equivalent of 1HUL, 2HUL or somewhere in between? Does it matter if you are looking directly at the LEDs or at a surface being illuminated by them?

I've used 25 fps here since with cartoons a frame rate above 25 fps creates a moving image... it may be a red herring.

Tips for university teaching

onoclea — Wed, 12 Dec 2007 12:25:09 -0800

Teaching a university course for the first time: any tips or suggestions? A friend of mine is preparing to teach his first university course, calculus for non-math majors. He has given single lectures and many seminars before on other more advanced topics, but this is the first time he will be carrying a whole course, on calculus, and with an audience of this size. He's a quiet guy, works really hard, takes this commitment very seriously, wants to continue in academia, and obviously wants to do a good job! Any tips, suggestions, warnings, recommendations, revelations, wake-up calls, etc. would be very much appreciated! Thanks.

Why the inconsistent derivatives?

PuGZ — Sat, 03 Nov 2007 01:01:37 -0800

Where am I going wrong with this (very simple) implicit derivative? I have an equation: xy + y^2/x = 2. I solve it this way:

(1 * y) + (x * dy/dx) + (2y*dy/dx * x^-1) + (y^2 * -x^-2) = 0
dy/dx(x + 2y/x) = y^2/x^2 - y
dy/dx((x^2 + 2y)/x) = (y^2 - x^2 * y)/x^2
dy/dx = (y^2 - x^2 * y)/(x^2) * x/(x^2 + 2y)
dy/dx = (y^2 - x^2 * y)/(x^3 + 2xy)

Now, the answers I have before me say the correct method is:

x^2 * y + y^2 = 2x
(2x * y) + (dy/dx * x^2) + (2y * dy/dx) = 2
dy/dx(x^2 + 2y) = 2 - 2xy
dy/dx = (2 - 2xy)/(x^2 + 2y)

Both of these appear correct to me, but the end result is different in each case? Can someone explain the ludicrously obvious mistake I am making?

Maths: Help me!

cholly — Wed, 24 Oct 2007 18:26:57 -0800

Time for a ridiculous math question: I've got F=255M^(-1.08) and I need to work out M. It is driving me crazy that I can't work this out.

[[not a homework question]]

Thanks in advance!

Inequalities and direction-flipping

PuGZ — Fri, 19 Oct 2007 22:00:46 -0800

Why is it that when I solve the inequality 0 ≤ arccos(x) <> cos(π/4)? Why do the operators switch direction? I understand that when multiplying or dividing by a negative number, the operators switch direction - but why is this the case for functions?

mathematics chess book?

randomizer — Thu, 18 Oct 2007 16:21:49 -0800

is there a book on the mathematics of chess? i've been looking for a book that deals with the mathematics or/and game theory of chess, but i'm not having much luck. is there a chess book that deals with the mathematics/game theory?

Difficult as ABC

londongeezer — Sun, 16 Sep 2007 14:35:54 -0800

ABC x D = BADC. What single numbers (1-9) do the letters represent? Is there any way to arrive at the answer (a) by logical deduction all the way rather than with some trial-and-error and (b) so that a 10-year-old can follow the logic? By trial-and-error I mean, for example, having deduced that C might be, e.g., 5 (whereas it couldn't be, e.g., 3), then experimenting with various values for D (3, 7, 9) and so on. That's one way to get to an answer, but I'm hoping there's a more purely deductive route.

Equation solving help for the intellectually challenged

prentiz — Mon, 04 Jun 2007 06:49:22 -0800

(x + y)-(x*y)=79. What are x and y? I know that, once upon a time I knew how to do this - sadly it must be in one of the parts of my brain knocked out by decades of alchol. Apparently neither are allowed to be 0 - which ruled out my boss' solution. Any help much appreciated - particularly if you show your working out!

Math makes my head hurt.

Optamystic — Fri, 18 May 2007 03:52:16 -0800

Maths Question. Company has 100 shares. Company needs to issue additional shares to Person A so that Person A holds 20.83% of all shares in Company (taking into account his original shares held, and his new share allocation). How many new shares should be issued? (Rounded to the thousandth of a share).

The Various Workings of a Cube-Shaped Gallery

0bvious — Tue, 24 Apr 2007 18:14:20 -0800

Imagine a cube-shaped building, with ten cube-shaped rooms along each side (10 rooms long, 10 high & 10 deep). Each cubular room has 4 walls, 1 ceiling and 1 floor. Each of the 6 interior surfaces in all 1000 cubular rooms is decorated with a different piece of art. The rooms can be moved around the building, as if it were an enormous Rubik's cube, but they can also be spun on their axes, so all 6 walls of all 1000 cubes is capable of touching all the others (if the cube is so arranged). How many combinations of art within the 'Cube Gallery' are possible? If you can run me through the workings of the maths I would be extra grateful. Also, what technical words/phrases/language are useful/interesting in expressing this concept? To restipulate the numbers:

- A cube gallery with 10 cube rooms along each side (10x10x10)

- Each cube room has 6 pieces of art on its interior surfaces

- All the cube rooms are capable of being rotated into every possible variation (ceilings becoming walls becoming floors etc.)

Thanks in advance!

The stats of bowling 300

roofus — Mon, 19 Feb 2007 15:14:14 -0800

ProbabilityFilter: Can I predict, from my bowling average, how many games it will be (on average) until I bowl a perfect 300 game? There must be a fixed, but non-linear, relationship between bowling average and likelihood of bowling a perfect game. Assuming I don't choke on the 12th strike, can I work out how many games it will take me to achieve perfection? My maths skills have failed at the stage of trying to convert my average into a strike percentage.

How do I calculate GPP on goods sold?

tomble — Sat, 09 Sep 2006 17:36:34 -0800

How do I calculate Gross Profit Percentage (GPP) on goods I sell? I've tried google but it has confounded my limited maths skills.

I want to calculate GPP on goods. I have the cost of the goods, the sale price, the gross profit, but I don't remember how to get the GPP figure.

Cost : $5.00
Sale : $12.00
Profit : $7.00
GPP = ?

I know this is really simple, but I can't remember how it's done and I really need to get it right.

Too lazy to take a hard-right.

Jimbob — Fri, 25 Aug 2006 04:45:21 -0800

Do the curved triangular shapes made when cars (or even pedestrians) take "shortcuts" at T-junctions (seen here near my house and here in Western Sahara, although this seems like a deliberate one) have a name? What's the mathematics behind them? The psychology?

Help me understand modulus operators

TheDonF — Tue, 08 Aug 2006 06:17:19 -0800

My maths skills are rubbish. Help me understand modulus remainders I'm working my way through some JavaScript stuff and have seen the modulus operator used quite a bit. All well and good, but it doesn't make sense. It's supposed to return the remainder after a division, so I can see why 9%3 (9÷3) is 0. But, if 12%100 is 12 (12÷100 = 0.12), why is 1%2 1 and not 5 (1÷2 = 0.5) and why does 8%3 = 2 and not 66 (8÷3 = 2.66)?

Quick maths question!

PuGZ — Sun, 30 Jul 2006 03:42:10 -0800

Quick maths [very basic trigometry] question. If cos(x) - sin(x) = 1/4, what is x, and therefore cos(x) * sin(x)? How do I go about working this out? I'm highly embarrassed that I can't work this out myself. Thanks!

Surviving a Total Perspective Vortex

0bvious — Sun, 09 Jul 2006 08:39:35 -0800

I'm on the hunt for sites and/or blogs about big ideas... Who wants to join me? I am interested in the nature of the human, the self, consciousness, space-time and infinity, the future, cultural evolution, the emergence and destruction of civilisation, physics, biology, technology, science fiction, this self perceiving universe, the narrative, the protagonist, belief, faith and the Gods, mathematics, language, truth, semiotics, theory of mind, theory of relativity, philosophy, transhumanism, the base of humour, of love, of art, of literature, chemistry, the stars and how they shine, justice, anger, naivety, pop-culture, culture shock, poetry, evolution, devolution, darwinism vs subjectivity, how to and how not to, how it is, how it could have been, perspectives of 'the idea', how the perspective shifts, surviving a total perspective vortex....

I want to find people who find these things interesting too, I want them to come over and chat liberally with me, with my like-minded associates, with other web-portal psychonauts.

Apart from Metafilter where do you get your intellectual, mind exploding fix? Where should I begin my search for new minds to meld with?

Maths powers failing me...

prentiz — Mon, 24 Apr 2006 07:31:29 -0800

Maths question: How can you make 25 using only the numbers 2,4,6,8? A friend of mine has been stumped by this - and as a mathmatical illiterate so am I. Apparently you can use each number once and there is no requirement to use all of them. I am assuming there is some sort of cunning trick at the heart of this...

A physics question. And no, you aren't doing my homework.

alby — Wed, 04 Jan 2006 13:14:06 -0800

Two objects, both mass 1kg are placed 1m apart in a total vacuum. How long would it take for the force of gravity to pull them together (assuming no other forces act)? I've been trying to solve this iteratively by spreadsheet but I know there must be a proper integration/maths answer.

simplifying ratios and fractions

lunkfish — Sat, 17 Dec 2005 03:35:33 -0800

Is there a mathematical technique for simplifying ratios/fractions? This sounds searchable I know, but I can't find anything. If you've got 4/12, you can see that it simplifies to 1/3, but is there a way you could work out that 168/504 simplifies to 1/3 with pen and paper?

I think finding the lowest prime number they can be divided by would be one way but I don't know a way to work this out.

If anyone has some good links for maths and physics questions involving ratios/fractions that would be cool.

Help me with maths / betting

priorpark17 — Thu, 15 Dec 2005 05:46:30 -0800

Need someone to do a bit of maths for me: There is a stupid TV show that I bet on. It is called celebrity come dancing where couples ballroom dance. Anyway I bet on Zoe Ball & Ian Waite at 14/1 earlier in the year. There are now three couples left and the odds are as follows:Colin Jackson & Erin Boag 4/6; Darren Gough & Lilla Kopylova 11/4; Zoe Ball & Ian Waite 3/1. How much should I bet on the other two couples to guarantee the best return whatever happens in this weeks final. Maths was never my thing ( as i am sure you can tell).