Formerly good at math, but I've lost my skills. Any advice to grow them back?
math.stackexchange.com
math.stackexchange.com
...until I picked up some stuff that I'd thought was hard in college. I was dumbfounded at how easy it was. What had changed was not my math abilities, but my perception of what constituted hard math.
When you're in high school, you don't realize how much of a gulf there is between Ph.D/MS-level (or even professional-level) math and what you learn in school. The public school system teaches you the barest foundations; there's a gigantic world out there beyond it.
A few days ago I brought out Learn You A Haskell and took a look at the monad section and suddenly it all made sense. Sometimes your unconscious needs time to digest concepts and internalize them before you can master them and move on to hairier problems.
In high school and even the first year of university I was pretty much a natural at math. I'd been doing algebra and trigonometry since I was 10, calculus since I was 13 and started on differential equations at 15.
Not that this made me any kind of child prodigy mind you but it was a fairly isolating experience because my first 18 years took places in isolated towns with <15,000 people so I just didn't come across other people like me or with similar interests. But I digress...
The second year of university maths bored me senseless and it sucked all the fun out of maths for me. Three hour proofs, numerical methods (in particular) and so on. So I stopped doing it and just did CS instead (originally I'd been intending some kind of double major equivalent).
Having not used calculus (for example) for years I can still remember how to derive/integrate, etc. So I retain a decent part of what I knew (or so it seems). But the one area I suffer in, largely because I never got that far, is in deciphering academic papers. This applies to CS too, which is where it's a pain.
I like dealing with actual code rather than abstract ideas put in text (and the vaguest of algorithms that you can't just take an implement, or at least I can't).
So my situation isn't identical to yours but I really would like to know how I could improve my maths and CS in this area.
Academic papers are written from the far side of that roadblock. They're often best considered anecdotal pointers to how to survive abroad rather than comprehensive guides like textbooks (or review papers) offer. Reading them is thus both an exercise in deciphering something distant from your comfort zone and learning to apply its vague knowledge to your own situation.
In order to understand academic papers then, you've kind of got to become a traveler yourself. At that point you appreciate the vague note passing because even though it's difficult, there's a real opportunity there to see something few ever have before.
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So practically, academic papers are never easy to decipher unless you're basically part of the same communities as the authors (or they are really dedicated and skillful communicators who have an uncommonly deep understanding of the topics they're writing about). If you're doing work that cannot be solved by what exists and is common knowledge today, however, they're your best bet at finding a guide and no matter how difficult they are you want to read them through.
There was a room of 4 males and 10 females, now there was 5 other guys who were to be paired with someone in that room. What is the probability that the pairs would be as follows (MM,MM,MM,MF,MF) where M=Males and F=Females.
This was a real life problem I create for myself to determine the bias by the selector. I struggled to work it out by pen and paper. This was a problem 8 years ago it wouldn't take a minute to do, most of the work would be in punching numbers in the calculator. Eventually, I said when I go home I will program it up. Between the time it took for a friend to restart her computer, I had whipped up a simulation. This is something I wouldn't have been able to do 8 years ago.
So in a sense, I call it a skills exchange. I lose some skills and gain some skills. I'm sure with practice I would be back up to par, the same goes for this guy.
If what you want to know is the probability of having the 5 guys paired with 3 men and 2 women (which is what I think the grandfather meant), the answer is
C(4,3) x C(10,2) / C(14,5) = about 9%
(number of ways to pick 3 men out of 4 x number of ways to pick 2 women out of 10 / number of ways to pick 5 people out of 14, /regardless of the order/)
If you want to know the probability of having the pairs made exactly in the order the grandfather mentioned, it's
P(4,3) x P(10,2) / P(14,5) = about 0.9%
(as above, but considering the order)
where C(M,N) and P(M,N) are the number of combinations and permutations of N items out of M, respectively.
(edit to change multiplication symbol, asterisk doesn't show)
The hard bit is having the intuition to see that this is right, which is just what Bill Dubuque's answer goes on about in the linked article.
I went from sucky math guy to an awesome math guy in just 1 year - just because I was tutoring.
You should be able to run through the set without much effort, but I think there is value in doing these simpler exercises. It establishes routine and steeps the mind for greater challenges.
I will likely add some permutation & combination stuff to my 'course work' before I go on to my eventual goal of understanding prob & stats. Getting exercise for these higher level topics will be a challenge.
http://www.greenteapress.com/thinkstats/html/index.html
I've also been studying a berkely stats course on itunes u and working the exams/notes from this class:
https://netfiles.uiuc.edu/fenghong/www/STAT100/
I'm also reading a lot about financial analysis and risk assessment to fiddle around with real-world applications of the things I'm learning.
it's a hell of a journey.
Which is to say, I highly suggest doing this stuff as long as you get value out of it. It'll be a boon to your comprehension speed later.
Eventually, however, go find a hard textbook and work through every single line of it. Really. Understand that it'll possibly take years and involve finding many lesser sources to fill in the gaps, but without a hard motivating problem you're going to get stuck in an affective loop on formulaic knowledge. Easy, satisfying, but somewhat flat.
These solutions can definitely be abstracted out to other areas, but really--what part of math can't?
And he will have to accept lots of failures before he can start to claim lots of successes. With nobody to mark his efforts down for not showing sufficient workings, however, admitting to failure can come a lot more easily when you only have your own self as teacher and student.
On a side note, we've been arguing about 48÷2(9+3) at the office today. There is a correct answer, of course, but also an argument (that some think is reasonable) against that answer.
If anyone cares. We can poll it up.
to clarify: PEMDAS is the order of operations. so parenthesis first: 48÷2(9+3) = 48÷2(12) then multiplication and division (they have the same precedence): 48÷2(12) = 24*12 = 288
for another reference: http://www.google.com/search?q=48%C3%B72(9%2B3)
http://www.physicsforums.com/showthread.php?p=3235154
Anyway, the answer depends completely on whether you believe that multiplication by juxtaposition has the same precedence as multiplication by explicit symbol. There're good reasons to believe it doesn't, eg. the first post on that linked thread, but whatever the answer, it's entirely based on typographical convention. I don't work in the community that cares, so I don't really have an opinion, other than to point out it's not as cut-and-dried as virtually ever poster here believes.
In the community that I do work, people who write parsers, things like this have to be explicitly specified. That's why I maintain that the correct answer is "syntax error".
sent frim my drunk phone
It's like this: if you study a language intensely for a year, you'll have a good understanding of it after that year. If you stop using it, the grammar will remain with you but your vocabulary will fade over time. If, however, you travel back to that country, it'll only take you a couple weeks to regain took you a year the first time around. Math is a language, and what you lose is vocabulary, not the language itself.
I'm 27 and have been out of school for 5 years. I couldn't do integration by parts without consulting a textbook, and I'd probably do poorly on a Calc-3 final if I had to take it closed-book, right now, in the alloted time. But I also know where to look when I need to review calculus or linear algebra. There's a huge difference between "rusty" and lost skills.
For "rusty", you just need to study again. It starts out hard and gets easier as you regain the skills. It's actually fun, at least for me, to revisit familiar friends like set theory. And I'm still learning new things (although not at as fast a rate as when I was in school) even though I've been out of school for half a decade.