How fast can you do mental Math?

January 17th, 2008 | by Sol |

There’s an interesting web-site, brainetics.com, that is all about doing mental Math quickly. I have to confess that whilBraineticse I know quite a few mental Math tricks and while I’ve written quite a number of posts and made several videos about mental Math tricks I’m not particularly fast at applying these tricks. Doing Math quickly in one’s head is all about knowing techniques, having a strong memory and maintaining focus. I know techniques. Memory and focus are currently a challenge for me.

Brainetics sells a $180 product geared to improving mental Math abilities. I’m not rushing to spend $180 to see how helpful Brainetics might be but I’d love feedback from anyone who has used the product.

A free resource on the Brainetics site is the Brain Games page. Near the bottom of the page is a link to a game, Brain Burst. The game has two levels, hard and harder. The first level gives you a bunch of two-digit by two-digit multiplication problems. Possible answers are floating on the screen. You get points for clicking on the right answer quickly. You lose points for wrong clicks. If you are slow to answer then incorrect choices start to disappear, making it easier to get the right answer but, I imagine, losing you points.

My highest score was 29 points on the “All Star” level, which is the easiest of the two. I suspect many of you could do better. I found that racing against the clock was mentally stressful even though I know how to do 2×2 digit multiplications in my head. Brainetics may have a better approach than I have to this kind of multiplication or they may have a good approach to holding the partial product in your head while you work on more of the product.

If you want to try this game and don’t have an approach to mental multiplication I suggest this for the 2×2 digit case:

To multiply numbers with digits ab and cd together:

  1. Multiply bxd. That’s the last digit. There may be a carry you’ll have to remember.
  2. Multiply adxbc and add the carry to get the next digit. You may generate a new carry.
  3. Multiply axc and add the carry to get the rest of the answer.

As an example, to multiply 12×34:

  1. 2×4 = 8. 8 is the last digit.
  2. 1×4 + 2×3 = 10. 0 is the next digit. 1 is the carry.
  3. 1×3 = 3. Add the carry of 1. 4 is the leftmost digit of the answer.
  4. 408 is the answer.

I found myself using the strategy of guesstimating answers. That helped sometimes, although sometimes two of the possible answers were close to one another.

I’d be interested to know how others do with this game? Do we have brilliant mental mathemagicians among us?

If you’re interested in learning more mental Math tricks check out my related articles and videos:

Also, check out a couple of Dave Marain’s recent explorations on mental Math at his MathNotations blog:

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  1. 15 Responses to “How fast can you do mental Math?”

  2. By Mike on Jan 18, 2008 | Reply

    Its a fun game :) - I played it 3 times and got 29 points each time using a guesstimation strategy. This works quite well a lot of the time but, as you mentioned, it fails when you have 2 answers that are around the same magnitude.

    I wish you hadn’t told me that you got 29 points though because now I just HAVE to keep playing until I beat it.

    Now if only I can get it working on a handheld device….

  3. By Sol on Jan 18, 2008 | Reply

    Mike,

    I wonder if the score is stuck at 29. It always told me my score was 29 and I just assumed it was reporting my high score. I’d be interested to hear if others get different scores.

  4. By Rio Armijo on Apr 21, 2008 | Reply

    please come to our school

  5. By Anonymous on May 25, 2008 | Reply

    I COULD BEAT ALL YA THAT WHO THINK THEIR THE BEST

  6. By BRANDY P on May 25, 2008 | Reply

    Im very fast at math but I just see that very close

  7. By melissa elana on Jul 3, 2008 | Reply

    you cant beat anyone no one is perfect

  8. By brittany on Nov 21, 2008 | Reply

    i think all those commonts are really good and nobodys perfect you gotta work it dog

  9. By Joell Burville on Jun 5, 2009 | Reply

    In your first example, it doesn’t seem that your direction #2 and your example of #2 compute: (”2. Multiply adxbc and add the carry” and, “2. 1X4 + 2X3 = 10. 0 is the next digit. 1 is the carry.”) Your example is correct, but your direction isn’t.

    The DIRECTIONS are wrong or at best unclear; the ‘EXAMPLE’ is correct but doesn’t seem to follow what you have directed.

    In your first illustration on your site, I think you’ve made a mistake in the DIRECTION number 2. (”Multiply adxbc”) In following it, it was quite confusing to me how you came to your conclusion of the number 10 in your example. What you should have written IN THE DIRECTION PART is: (aXd)+(bXc) which is, as you wrote in the example part, 1×4+2×3=10. A PLUS sign not a MULTIPLICATION sign in the middle. (1×4 PLUS 2×3=10 —ad+bc, or aXd+bXc=10). The way you wrote the DIRECTION works how? “Multiply adxbc” ???? What does that mean? That would/could be: (1×4) x (2×3) which would be (1×4=4) x (2×3=6) which would be 24 not 10. The multiplication sign X should have been an addition sign +. The mulipication was of the first and fourth numbers (1 and 4) and the second and third numbers (2and 3) then you ADD those two products together, NOT MULTIPLY them. Nowhere does it imply that in your DIRECTIONS. That direction in #2 is sooo unclear to me. I think that in order to translate the directions on our own for other examples, we need clear and correct directions. I haven’t read past the first illustration to see if there is any more directional mistakes but I’ll write again if there are. VERY interesting site. Thanks, Buzzybee

  10. By justin on Sep 18, 2009 | Reply

    I usually do this:

    say 12 * 34

    In my head, i do 10 * 34 + 2 * 34, which is usually 2 easy multiplications, and one addition. This works well for me, because you don’t have to store large amounts of numbers for long - really, you do the easy multiplication first so that it persists in memory before it dies, and you do the second multiplication fairly quickly - by this time, you only remember two numbers, and we all love addition which is fairly easy.

  11. By c on Oct 25, 2009 | Reply

    you mean to multiply the 2 X 34 then add the two products. If you simply add 2 the answer is incorrect.

    12 X 34 10 X 34 = 340 + 2 = 342?

    12 x 34 10 x 34 = 340 2 X 34 = 68 now add
    340 and 68 = 408

    I think that’s what you meant to type. It works!!

  12. By selva on Dec 13, 2009 | Reply

    hahahaah
    >>>>>>>>>>>>>
    To multiply numbers with digits ab and cd together:

    Multiply bxd. That’s the last digit. There may be a carry you’ll have to remember.
    Multiply adxbc and add the carry to get the next digit. You may generate a new carry.
    Multiply axc and add the carry to get the rest of the answer.
    >>>>>>>>>>>>>

    If this is a fast multiplication tecnique….I wonder hw u do the long one….ABACUS??? lol

  13. By Summer on Dec 19, 2009 | Reply

    All of this multiply ABxCD is just FOIL backwards (LOIF) . In algebra I think, FOIL means First, Outer, Inner, & Last. Therefore if you take 78×96 and use LOIF (FOIL backwards) you would multiply the last digits of both numbers 1st (8×6=48). The 8 would be the last digit and the 4 would be the carry. Next you multiply the outer #’s, then multiply the inner #’s and add the results together. DON’T THE TO ADD THE CARRY TO THE RESULTS (7×6=42 + 8×9=72…. 72+42=114+4(the carry)=118. The number that goes in front of the last number is 8 and the 11 is the carry now. The final step in this equation is multiplying the front digit together (7X9=63) and adding the carry to the answer (63+11=74) The 74 goes in front of the 2nd 8 giving us the answer of 7488. 78×96=7488. I thought this may help if the abxdc seems a bit confusing or more difficult.

  14. By Summer on Dec 19, 2009 | Reply

    Sorry for the error in typing. I meant to say DON’T FORGET TO ADD THE CARRY TO THE RESULTS.

  15. By myquisha on Jan 11, 2010 | Reply

    hahahahahaha no i ccan beat anyone…..who try me…..probably not mike you just to good

  16. By kevinkendall on Feb 5, 2010 | Reply

    hehehe
    I could beat YOU in an English sentence structure/grammar/spelling quiz, I be purty sure ’bout dat one.
    hehe
    So you not all dat bad, man.

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