Comment on Ethiopian MultiplicationComments−aaronbrethorst14yTo multiply 14 and 12 in my head, I break it down like this: 14 * 12 = (14 * 10) + (14 * 2) = 168 Anyone else do that?−Someone14yNot for 14 times 12, as that is (13+1) times (13-1). 'everybody' knows 1^2 = 1 and 13^2 = 169, so 14 times 12 = 169 - 1 = 168.−ljd14yYes, I process everything in 10% as well. 15% tip on $34? 10% = $3.4 so half of 3.4 is 1.7, combine them for $5.10.−barking14ySometimes. Or to multiply by 25, multiply by 100 and divide by 4. I always meant to study the trachtenberg method but never got around to it−ajuc14yI do this sometimes.Sometimes I refactor at first: 14*12=28*6=56*3=56*2+56=112+56=168 or 14*12=7*8*3=21*8=160+8−jcr14ySimilar here, but based on memorization. Since I know twelve squared ((12 * 12) = 144) by rote, the rest is easy. 14 * 12 = (12^2) + (12*2) = 168−drharris14yI tend to use the tens as well, but in this case I would have used the 12*12 + 24 trick. I also use some of the others listed here, so it makes me happy to know there are people like me out there.
Comments
To multiply 14 and 12 in my head, I break it down like this:
Anyone else do that?Not for 14 times 12, as that is (13+1) times (13-1). 'everybody' knows 1^2 = 1 and 13^2 = 169, so 14 times 12 = 169 - 1 = 168.
Yes, I process everything in 10% as well. 15% tip on $34? 10% = $3.4 so half of 3.4 is 1.7, combine them for $5.10.
Sometimes. Or to multiply by 25, multiply by 100 and divide by 4. I always meant to study the trachtenberg method but never got around to it
I do this sometimes.
Sometimes I refactor at first:
orSimilar here, but based on memorization. Since I know twelve squared ((12 * 12) = 144) by rote, the rest is easy.
I tend to use the tens as well, but in this case I would have used the 12*12 + 24 trick. I also use some of the others listed here, so it makes me happy to know there are people like me out there.