Multiplication Tips

I'll admit this is way slower.
104
x 105
------
10,920

All you do is put a 1 for the first number since it always be that, then add the last numbers together and if it's one digit just add a zero in front then multiply the last numbers together and that's your answer.
Only works for numbers 104-109

It's the same as the traditional method. Not faster at all.
You simply "cheat" by doing mental addition for the two middle steps.

I too learned the long, long, method in the 70's. This is much more efficient. Sure it takes a little mental power to sum the products, but it's less of a mess than what I was taught. Well done charlesblu99

Apu

Bad and confused explanation!

probably for 2nd grades

why put 2nd grade math on youtube? this is gay

I'm confused

this is way better to try in the mind than the traditional way.

if I knew this in school NO they did not use this method just the basic multiply down.

Isn't this how we learn in elementary school? Just instead of calulating all the sums in mind, we wrote it down, and add up at the end. It's the same, not any faster.......

...I think I've asked a stupid question. ...Don't worry about it.

Thanks for the video, I've learned from it!

Hey, "charlesblu99", is that you in the video?

this is awesome man.....! thanks!

This is why we should vote for someone who'll cut defense spending and increase education investing. We NEVER learned this method in any school I attended when I was a kid (yeah, it was in the 70's and 80's). Consequently, I hated math and economics which is full of math. The only thing I kept was figuring percentages with cross multiplication. Those who have learned this early on, consider yourself fortunate. Thanks for sharing this :)

Lol. U sound indian.

very good!

Yes, but mental math does get easier with practice. We got drilled in primary school, and I feel better off for it.

Oops, apparently YouTube doesn't like the <sup>tag.

Anyway...as for doing 42^2 and 38^2, I basically mentally rewrite it as (50 - x)^2.

(50 - 8)^2 =
50^2 - 2 * 50 * 8 + 8^2 =
2500 - 800 + 64 =
1764

The key is by subtracting/adding from/to the nearest 50, I force that middle (2 * 50 * x) term to be divisible by 100. This means I can mentally keep track of the digits, since only with the last term do I have anything in the tens or units place.</sup>

The first one (387 * 463) I did in my head in about 30s by mentally rewriting it as (425 - 38)*(425 + 38) = 425²-38².

Squaring numbers that end in a 5 is easy. Take the tens digit multiplied by itself plus one and postpend a 25 on it (35² = 100*(3*4)+25 = 1225).

42² = 1764. 1764+42 = 1806 -> 425² = 180625

38² = 1444

180625 - 1444 = 179181. The subtraction is the hardest step.

in poland this "method" is teached in elementary school ^^

It looks cool, but my concern is all the mental math it takes to do all this to begin with.

that was pretty awsome...

OMg lol ty im only 9-10 and i understand it :DD

wtf?.. this is what we have learned in third or fourth class?! :))