mental math

[DNS]

Nas Daily's video today:



That's the way I would add too, but I'm no where as good as this guy. The key is just going left to right. For example:

54
+47
+63
+75
======

Just add up the left column first:
50+40+60+70 =220 (whole, round numbers easy to do in your head)
then the right column
4+7+3+5=19

220+19=239

Easy, once you know the trick.

[Miorita]

It's called Arithmetic.

Miorita

[DNS]

It's called Arithmetic.

Miorita

Correct, the more advanced math is what is really math; trigonometry, calculus, etc.

But in colloquial usage, people refer to it as math or in this case, mental math; doing the arithmetic in your head, no paper, no pencils.

[Nicholas]

The point Miorita missed, (for the only time of course) is that Arithmetic was taught until recently thusly:

54
+47
+63
+75

Add the right column first, 4+7+3+5=19 - then put down 9 only and carry the 1 to the top of the left column. Then add those four digits to the 1 and get 23 which you write down to left of the 9, voilà = 239.

But this new method is quicker, unless you are used to the way you were taught as a child.

[Miorita]

He does this out of fear.
In case anyone catches him, he tells them he's done his math.

[DNS]

He does this out of fear.
In case anyone catches him, he tells them he's done his math.

Fear of what? No, I think he's just good with numbers and the mental way of doing it left-to-right. With practice, one can get pretty good at it, although I don't know if there's anyone better than this guy (in the video).

[DNS]

When my kids were young, I'd play a game with them:

Start with 2.
Double it. (no paper, no pencils)
Have a referee who checks with calculator.
Keep going until someone gets the wrong answer.
For example, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, etc.
Sometimes we'd get up to 524,288 and then one of us messes up.