I'm taking this math class at Winthrop! It's really cool...we are doing some very hands on math activities every day and I LOVE it! I can't wait to teach my students some of the things we've learned in this class.

One of the coolest things we've learned is called chisombop. Are any of you familiar with this? I didn't know it was called chisombop...I just thought it was a 9s multiplication tables trick. It's when you number your fingers and thumbs from left to right...1-10. Then you fold down the finger that corresponds with the number you're multiplying by 9. The number of fingers up to the left of the folded finger is the tens and the number to the right of the folded finger is the ones.

Example:

In this picture, Sarah's fingers will be numbered 1,2,3,4,5,6,7,8,9,10, from her left pinky all the way to her right pinky.

In this picture, Sarah's #3 finger is folded under. The multiplication problem would be 9x3. Look at the number of fingers unfolded to the left of her #3 and count them. You should see two. Now look at the number of fingers unfolded to the right of her #3 and count them. You should see seven. The fingers to the left of the #3 represent the tens and the fingers to the right of the #3 represent the ones, thus the solution to the multiplication problem 9x3 is 27.

This works with all the 9s multiples up to 10! How cool is that?

There's another one that I learned that's even cooler, but it's way more complicated and will take another post.

Thanks Dr. Mink!

## 7 comments:

I have always loved this trick since I am awful at math! Never knew it had a name though! Cool stuff!

HI- I came across your blag from Nate's, and saw Rock Hill!!! We lived in Ft Mill before moving out here to the island and I miss my old friends, church and all... ;)My middle little girl will be in 7th grade new year- 3 of our kids are from Ethiopia and are doing really well- learning English and in all of their classes- anyway, I just wanted to say hi!! Blessings to you.

This trick is my handicap in math. I teach my kids it every year, knowing that I literally still have to do it to this day in order to recite my 9's. Don't tell my principal that I don't know my 9's. I blame my 3rd grade teacher.

This is Lindsey by the way. I also don't know how to sign my name. Sorry.

That's not Chisanbop (note spelling). In Chisanbop, the tens digit is done entirely with one hand, and the ones digit done entirely with the other. The thumb counts for five, and the other four digit count as one.

There are courses for Chisanbop, and a couple of books were published on it if you're interested.

Postscript--Chisanbop is basically an application of abacus techniques applied to the human hands. There have been people who can get answers to very complex mathematical formulae faster than a person can on a calculator.

My entire class was taught this in 1981. To this day, I have to count by Chisanbap to figure out 7+5. I definitely do not recommend teaching kids this. While it seems really cool (and I rely on it), I think it actually can hinder kids/adults in the long run.

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