My Dry-Erase Board And A Math Trick!

[brokencirkle]

O.o whoa

[CelesChere694]

That will come in very useful in my Physics class.

[manaros]

but the square of 12 is 144 while in ur way is 24 is that onnly if the last number is 5??? nice try!!"=)

[willdawg840]

yea..if u read the info and listened he said that it's only for numbers that end in 5

[Fennicus]

nice vid, the sound quality wasn't the greatest though :P

[saori90]

does 777 edd with 5?

[souldemolisher101]

wow thats awsome

[opinionhead444]

Proof for this trick...

ab * ac where ab & ac are two-digit numbers, and b+c=10.

In reality, (10a+b)(10a+c) = 100a^2+10ac+10ab+bc

Some reverse distributing, 10a(10a+c+b)+bc

Since b+c=10 and b+c=c+b, then 10a(10a+c+b)+bc = 10a(10a+10)+bc = 100a(a+1)+bc.

This trick is only a corollary of that general rule the gentleman instructed upon.

[JealousGuy]

Hey, thanks! I'd never seen it proven before.

[2sssac]

it is only with the 5 at the end? i tried 72*72

[GodsRUs]

it works for any double digit numbers, with the 1st digits being the same and the 2nd digits summing up to 10.

ie. 43x47, just multiply 1st digit by next higher (in this case 5, so 4x5=20), and write the product of the last 2 digits (in this case 3x7=21)

and there you have it,

43x47=2021

[Mirado34]

Awesome!!!

[mustangspirito]

Try 777x777 it does not work guys!

[bjm4idplayer]

well, does 777 end in 5?

[Smilez78]

Ummm this only works with the last digit being 5

[teabowbraine]

im going to tell my math mate about that, he'll love it

[guywh0likscapncrunch]

nice. i'll use that for the number sense test

[Newbyneon]

Wo....your hand writing is amazing!

[ElveeKaye]

I see I'm not the only one who thinks so. Wish I could write with cool flourishes like that.

Oh, nice math trick, too. :o)

[smokeyinksmudge]

Wow... Cool..I love math tricks.. Hey, I like your handwriting style. Mine is like chicken scratches!

[mrdavesmagic]

That was a good one.

[maukrvp]

Nice, Have you ever heard of the rule of 72? That one can make you wealthy.

[Amazingspideyfan5]

math hurts my brain

[djairrick1200]

lol sniffing the marker!!