1...2...3...huh?

December 26, 2008 8:14 PM

Once upon a time I heard about a method of applying mathmatical operations (like multiplying 4 or 5-digit numbers together) using the knuckles of one's hands. Google has failed me. Did I imagine the whole thing? Assuming not, what is this called and how does it work?
posted by mezzanayne to Education (6 answers total)

I remember my mother teaching me the 9 times table using ten fingers held out, palms down. For 1 x 9, drop the left pinky finger, and there's nine fingers left. For 2 X 9, drop the next finger (left ring finger) so there's one digit on the left and eight on the right, making 18... and so on. But that's pretty basic, nothing like multiplying 4 or 5-digit numbers together.
posted by kaudio at 8:23 PM on December 26, 2008 [2 favorites]

Best answer: A Google search for "finger arithmetic" turned up chisenbop, an old method from Korea, and what appears to be a whole series of blog posts about another method. I remember seeing something about a system for finger arithmetic in an old library book, and I think the blog posts cover that. More fingers than knuckles, but maybe this is what you're thinking of?
posted by Quietgal at 8:34 PM on December 26, 2008

Response by poster: That's it, Quietgal, thanks so much! Any additional information or links would be appreciated.
posted by mezzanayne at 8:39 PM on December 26, 2008

You might be interested in Russian Peasant Multiplication, and Egyptian Multiplication. Not means of multiplying by hand, but fascinating methods nonetheless.
posted by Lemurrhea at 10:46 PM on December 26, 2008

Anecdotally, I was taught chisenbop in 5th grade and yes, it was tapping your fingers down, not knuckles...

Start with your right finger. Your index finger is one, your thumb is five. Yep, pretty much exactly what I remember is what's in the link above. I still do it sometimes. I remember the trick to learning it quickly was to count aloud as you tapped and if you did it sort of musically, it was easier.

I use it at least once a week when I'm counting characters and spaces for editing newsletters. I didn't know this was an unusual way of counting.
posted by Unicorn on the cob at 12:29 AM on December 27, 2008

its not mathematical but I remember when i was young learning how to figure out the # of days in the month by counting the knuckles

explanation from wiki
A language-independent alternative used in many countries is to hold up your two fists with the index knuckle of your left hand against the index knuckle of your right hand. Then, starting with January from the little knuckle of your left hand, count knuckle, space, knuckle, space through the months. A knuckle represents a month of 31 days, and a space represents a short month (a 28- or 29-day February or any 30-day month). The junction between the hands is not counted, so the two index knuckles represent July and August. This method also works by starting the sequence on the right hand's little knuckle, and continue toward to the left. You can also use just one hand; after counting the fourth knuckle as July, start again counting the first knuckle as August.
posted by ljesse at 9:10 AM on December 27, 2008