Mainly Mattias Posted January 15, 2013 Share Posted January 15, 2013 This seems so bloody easy! ..not to mention quick! Link to comment Share on other sites More sharing options...
n00bxQb Posted January 15, 2013 Share Posted January 15, 2013 My grade 8 teacher taught me that. I guess that would've been 16 years ago. Link to comment Share on other sites More sharing options...
Rounoush Posted January 15, 2013 Share Posted January 15, 2013 ...Okay, I'm just gonna say it: How does that work? Link to comment Share on other sites More sharing options...
n00bxQb Posted January 15, 2013 Share Posted January 15, 2013 ...Okay, I'm just gonna say it: How does that work? Link to comment Share on other sites More sharing options...
nucklehead Posted January 15, 2013 Share Posted January 15, 2013 As for quickness, there are quicker ways, especially on 2 digit x 2 digit multiplications. Link to comment Share on other sites More sharing options...
The Colt 45s Posted January 15, 2013 Share Posted January 15, 2013 I think I solved it in my head twice before he was done Link to comment Share on other sites More sharing options...
avelanch Posted January 15, 2013 Share Posted January 15, 2013 i would think that this would be stupidly slow for anything with more than 5 lines. or single digits. 9x9, for example, counting 81 intersections? no thanks. Link to comment Share on other sites More sharing options...
D-Money Posted January 15, 2013 Share Posted January 15, 2013 That probably works well for kids who respond well to visual aids. Me, I just always liked numbers, and never had a problem thinking in them. Link to comment Share on other sites More sharing options...
qball Posted January 15, 2013 Share Posted January 15, 2013 Mathematical models are great for helping kids to see the 'big picture' (what's really going on when we do stuff with numbers), but at the same time, they're rarely practical or efficient enough for general use... Link to comment Share on other sites More sharing options...
Heretic Posted January 15, 2013 Share Posted January 15, 2013 That probably works well for kids who respond well to visual aids. Me, I just always liked numbers, and never had a problem thinking in them. Link to comment Share on other sites More sharing options...
Mountain Man Posted January 15, 2013 Share Posted January 15, 2013 Calculators have always worked for me. Link to comment Share on other sites More sharing options...
GodzillaDeuce Posted January 15, 2013 Share Posted January 15, 2013 56 = 7 * 8 5, 6, 7, 8! Divisibility by 3: add up digits and check result for divisibility by 3. eg. 10,407 is divisible by 3 since 1+0+4+0+7=12 is divisible by 3 those are my math tricks lol Link to comment Share on other sites More sharing options...
GodzillaDeuce Posted January 15, 2013 Share Posted January 15, 2013 Same. I do it this way in my head: 13 x 12 = 13 x 10 + 13 x 2 13 x 12 = 130 + 26 13 x 12 = 156 Link to comment Share on other sites More sharing options...
D-Money Posted January 15, 2013 Share Posted January 15, 2013 This isn't really a trick, but is fascinating to me: Multiply any number by 9, then add the digits together. They will always equal 9, or a multiple thereof (18, 27, etc.) 9x2 = 18 ; 1+8 = 9 9x6 = 54 ; 5+4 = 9 9x17 = 153 ; 1+5+3 = 9 9x54 = 486 ; 4+8+6 = 18 9x238 = 2,142 ; 2+1+4+2 = 9 9x6,841 = 61,569 ; 6+1+5+6+9 = 27 9x483,902 = 4,355,118 ; 4+3+5+5+1+1+8 = 27 Link to comment Share on other sites More sharing options...
Mainly Mattias Posted January 15, 2013 Author Share Posted January 15, 2013 56 = 7 * 8 5, 6, 7, 8! Divisibility by 3: add up digits and check result for divisibility by 3. eg. 10,407 is divisible by 3 since 1+0+4+0+7=12 is divisible by 3 those are my math tricks lol Link to comment Share on other sites More sharing options...
nucklehead Posted January 16, 2013 Share Posted January 16, 2013 interesting! i'll remember that. don't know when i'd ever need it mind you.. maybe when splitting a dinner tab but i'd still prob end up whipping out the phone calc. lol Link to comment Share on other sites More sharing options...
-Vintage Canuck- Posted January 16, 2013 Share Posted January 16, 2013 I like how it says "(Warning: Math inside thread)". Link to comment Share on other sites More sharing options...
avelanch Posted January 16, 2013 Share Posted January 16, 2013 This isn't really a trick, but is fascinating to me: Multiply any number by 9, then add the digits together. They will always equal 9, or a multiple thereof (18, 27, etc.) 9x2 = 18 ; 1+8 = 9 9x6 = 54 ; 5+4 = 9 9x17 = 153 ; 1+5+3 = 9 9x54 = 486 ; 4+8+6 = 18 9x238 = 2,142 ; 2+1+4+2 = 9 9x6,841 = 61,569 ; 6+1+5+6+9 = 27 9x483,902 = 4,355,118 ; 4+3+5+5+1+1+8 = 27 Link to comment Share on other sites More sharing options...
Mainly Mattias Posted January 16, 2013 Author Share Posted January 16, 2013 You should never whip it out at the table.Bad luck. Link to comment Share on other sites More sharing options...
Evolution10 Posted January 16, 2013 Share Posted January 16, 2013 I like how it says "(Warning: Math inside thread)". Link to comment Share on other sites More sharing options...
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