Website review: Multiplication
IMAnerd discovered this in Mathematics
•24 reviews since Apr 9, 2005
mathematics, cartoons, math
•hunkinsexperiments.com/pages/multiplication.h...
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Reviews of this website
IMAnerd discovered 40 months ago- Too bad it's only useful for multipying number from 6-10.
- rssn rated 8 weeks ago
- I'm pretty sure people who needed to know how to multiple, just memorized it. There are only 15 combinations, of which 5 are multiples are 10. It would be much easier (and faster) just to memorize the other 10.
- Bongo23 rated 2 months ago
- nice
- meddlor rated 2 months ago
- This is a cute way to do multiplication. And for all the naysayers, it's actually useful for more than just 6-10, presuming you have fingers enough and/or don't mind a few negative numbers... The method presented here boils down to this computation: xy = 10(x' + y') + (5 - x')(5 - y'), where: x' = x - 5, and y' = y - 5. The person using this method takes the sum of the bottom fingers on either side (x' + y') and multiplies by 10. Then, adds in the product of the top fingers on either side ((5 - x')(5 - y')). The interesting bit is the multiplication by 10; why 10? Let's do some algebra: 10(x' + y') 10((x - 5) + (y - 5)) 10(x + y - 10) And now let's bring it all back to where we started: 10(x + y - 10) = xy - (x - 10)(y - 10) 10(x + y - 10) = xy - (5 - x')(5 - y') 10(x' + y') + (5 - x')(5 - y') = xy Bingo! 10 is selected because it is twice 5. So say you encounter a russian with n fingers, and he wants to multiply x by y. How would he do it? Setting aside all the finger twiddling and counting, he'd simply be doing this computation: xy = 2n(x' + y') + (n - x')(n - y').
- IronJeff rated 5 months ago
- I love his look of confusion in the second panel. IMAnerd, 6-10 are the hard ones. ;)
- Orion67 rated 9 months ago
- Ingenious! I've known about a trick for adding numbers up to one hundred using both hands, but this is one is quite interesting. Of course, multiplying two numbers less than ten is not that hard, but still it's a cool trick. Have to show this one to my kids.
- GWENHYFYR rated 17 months ago
- I sucked at math, if only I'd known this trick....well..... i haven't actually tried this..it looks too complicated...but if it works...that would be...fuck it...I'm NEVER GOING TO TRY THIS but I'm happy it worked for the russian peasants.
- rubyjules rated 19 months ago
- This is fascinating!!! Why couldn't they have taught me this in school?
