My Dry-Erase Board And A Math Trick!

	Duration: 02:55 minutes Upload Time: 2007-04-08 15:21:12 User: JealousGuy :::: Favorites :::: Top Videos of Day
Description: How to square a number that ends in 5. Without a calculator.
Comments
Fennicus ::: Favorites nice vid, the sound quality wasn't the greatest though :P 07-09-13 09:57:35 __________________________________________________
saori90 ::: Favorites does 777 edd with 5? 07-09-08 08:02:52 __________________________________________________
souldemolisher101 ::: Favorites ok i take that back..777x777 dosent work.....why dont you get high off that dry erase marker you virgin for life 07-08-21 20:03:13 __________________________________________________
souldemolisher101 ::: Favorites wow thats awsome 07-08-21 20:01:46 __________________________________________________
JealousGuy ::: Favorites Hey, thanks! I'd never seen it proven before. 07-08-05 05:55:15 __________________________________________________
opinionhead444 ::: Favorites 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. 07-08-04 13:59:46 __________________________________________________
2sssac ::: Favorites it is only with the 5 at the end? i tried 72*72 07-07-26 20:12:29 __________________________________________________
GodsRUs ::: Favorites 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 07-07-21 02:37:27 __________________________________________________
ElveeKaye ::: Favorites 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) 07-07-15 11:56:53 __________________________________________________
bjm4idplayer ::: Favorites well, does 777 end in 5? 07-07-14 00:11:18 __________________________________________________