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Weakness in mental arithmetic = weakness in math?

  1. Jun 17, 2009 #1
    Halfway through an undergraduate course in engineering, I'm now planning to review math fundamentals from pre-algebra, algebra, geometry to trigonometry and finally calculus because, as you may know, having a solid foundation in math is vital for any engineering course, and I've always been weak in math. I also happen to be very weak in mental arithmetic (adding, multiplying, etc. in head). Even a calculation as simple as 4+7 makes me think for many seconds, and when I can't figure the answer out I use my fingers to count! If this is for addition what can we say about subtraction? For addition involving two negative integers I always use the calculator so as not to make a mistake, even for such numbers as -7-3.

    Does having these problems impair one's ability to learn new math concepts? Should I improve on mental math before I start reviewing?
  2. jcsd
  3. Jun 17, 2009 #2


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    As an engineer, this kind of thinking isn't really that important. Seeing relationships between numbers, easier ways to multiply/add/exponentiate/etc. might be important in more of the realm of number theory or something, but not engineering.

    That said, if 4+7 takes you several seconds to compute, I imagine going through a numerical problem takes a lot of time. Simple mental computations arise everywhere in physics and mathematics, and the extra time I would imagine to be ridiculous. So for the sake of saving yourself time, I'd say it's a useful skill to practice.

    Don't worry too much though.
  4. Jun 17, 2009 #3
    But I can use a calculator. Can anyone imagine studying engineering without using a calculator?
  5. Jun 17, 2009 #4
    Mental arithmatic is not required in the slightest, convenient but not required.

    Its all about being able to maniputale formula correctly.

    Being good at mental arithmatic only requires practice. The only reason I became good at adding up quickly was becuase I worked behind a bar where you had to add up the prices in your head. Being able to add up 2 bitters and a gin and tonic, whilst pulling drinks and holding a converation, quickly became second nature.
  6. Jun 17, 2009 #5


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    Sigh, I guess. I was thinking in terms of something like factoring, differentiating, integrating, where there's quick arithmetic to be done. Or rationalizing fractions, multiplying by conjugates, etc. and I guess you can do all of that on a calculator. I'd argue it's faster (at present day) to do a lot of this in my head that type it into my TI-89. Also I find there's a much greater continuity of thought going through a problem pencil-paper-brain than with a calculator in hand.

    Of course this begs the discussion of what the hell is the point of learning it anyways when you can do it all on the calculator, but that's neither here nor there.

    The answer to the question of whether or not lacking arithmetic ability impairs your ability to learn math is a definite no in my opinion, but like I said, I find value in it.

  7. Jun 17, 2009 #6
    Weakness in mental arithmetic is something you can improve, but only if you want to. Using a calculator is the usual solution for anyone these days, including mathematicians (and math teachers). It is no longer necessary to know what 2+2 is. However, if you ask me, everyone should know, or be able to figure out the answer rather quickly, because it is elemental. It's like knowing the alphabet. I say even if you can do your job as an engineer, it is important to have the basic skill of addition.

    There is a book called "Speed Mathematics" by Bill Handley. It assumes some basics, but teaches you new and easier ways to calculate things (addition, subtraction, all of it). It's really cool. Maybe that could help.

    Don't loose sleep over this. I can tell you that 97^2 + 15 - 6^2 = 9,388 without using a calculator (seriously, I swear I didn't use one :smile:). Was it necessary... no.. of course not. But I worked hard in order to improve my mental ability, and the fact that I can do that makes me feel a little better about myself. You can too, if you want to.
  8. Jun 17, 2009 #7
    Can you say how many seconds did you take to do that one?
  9. Jun 17, 2009 #8
    About as many as it took me to type it out... so around 5.
  10. Jun 17, 2009 #9
    53^2 + 62 - 3^3 = 2898

    I took 1 minute 51 seconds to do this one, ending up with a wrong answer: 2571.

    Do you have any hope for me?
  11. Jun 17, 2009 #10
    I think some ability is necessary, but not too much. You should know how to go through the algorithms with pencil and paper... but in your head? I would say only order-of-magnitude calculations need to be done in your head, and those should be easy anyway (if they're not, you're doing something wrong).

    They do still teach the arithmetic algorithms in schools nowadays, yes?
  12. Jun 17, 2009 #11


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    No but I find it helps one concentrate on one's work better, double check an answer and even follow what the professor does in class!!

    I'm not demeaning anyone but I do remember an incident where the professor had something like [tex]1 = \frac{4 \mu_0}{2 \pi}x + \frac{1}{3}[/tex] then the professor said [tex]\frac{4 \mu_0}{2 \pi}x = \frac{2}{3} [/tex]

    and this kid asked how in the world did he get 2/3 from. Needless to say many people got a kick out of it.

    Learning to do mental arithmetic can save you many trivial steps especially when someone is trying to explain something to you. IMO its better that way because I used to be a tutor and I would pull my hair out when my students asked my to show a trivial step =(
  13. Jun 17, 2009 #12
    You betch-ya champ. :biggrin:

    I already mentioned it, but I should again. That book "Speed Mathematics" by Bill Handley is one of the best books ever written. I wouldn't be able to do that without reading that book.

    I'll show you a cool example on the back cover of the book.

    96 x 97 = ?

    The usual method of 7 x 6... carry the 4... and so forth is way too slow. There is an easier way. We use what's called a reference number (in this case, 100). It's hard to explain what that is, but you'll see after this.

    So, what we're going to do is subtract both 96 and 97 from 100.

    100 100
    -96 -97

    We end up with 4 and 3, respectively.

    Now, we subtract diagnally. Either 96-3 or 97-4. Either way, you get 93. (These are the basics you would make sure to know before moving on to this.)

    93 x 100 (the reference number) = 9,300. That's simple enough. You're just adding two zeros to 93.

    After that, we will simply add the product of the 2 numbers we found earlier (3 and 4) to 9,300.

    3 x 4 = 12 <--(basics, just memorize problems like these)

    9,300 + 12 = 9,312

    See. Easy, isn't it. With practice, anyone can do that mentally.
  14. Jun 17, 2009 #13
    Thats mega...
  15. Jun 17, 2009 #14
    Tell me about it. I nearly wet myself after I read that through the first time. It still gets me excited. :biggrin:
  16. Jun 17, 2009 #15
    I know that book, and I also have "Secrets of Mental Math" by Arthur Benjamin and "Shortcut Math" by Gerard Kelly, and both these books contain some pretty neat tricks to do mental math. However, the problem with these books is that they often show you how to do ridiculously large numbers, numbers for which someone would ask for a calculator 99% of the time anyway. And who would remember the steps for the example you showed? It may be easy using pencil and paper, but then doing it using the traditional method (right to left) is much easier, for me anyway.
  17. Jun 17, 2009 #16
    That's cool. I guess if you want the basics down, you could do something I used to do. You could write out a page of 50 basic math problems, and then time yourself on how long it takes to complete it. I remember I got about 23 seconds once on a 50 question multiplication paper (you know.. 5 x 7, 8 x 9). That's the most effective way I know of to memorizing and sometimes computing the basics.
  18. Jun 17, 2009 #17
    But all that apart, should I go ahead with my review without worrying about mental arithmetic, which perhaps I can improve on while doing the review?
  19. Jun 17, 2009 #18
    I would practice a bit before doing the review. I wouldn't think it would take long. Maybe a week of somewhat hard work and that should suffice.
  20. Jun 17, 2009 #19
    I've got only four months for the review, and I have to do a lot of things in it: algebra, geometry, not to mention calculus.
  21. Jun 17, 2009 #20
    I don't know what to tell you, other than I think its necessary. You should have enough time to work on it.
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