"" The Teacher in Me: Trick for Nines Multiplication Facts

Saturday, March 2, 2013

Trick for Nines Multiplication Facts

Have you ever heard of Grandma's Magic Math?  It is a book that is no longer in print but I have used the trick for the 9's facts from it for years.  "Grandma" drew a picture called the Nines River.  I can't remember exactly how her picture looked, so my students and I made up our own picture this year.  My daughter, who is in my class, made up a rhyme to help remember the numbers on the picture. The digits in a product of a x9 fact always add up to 9.  For example, 9x4=36, so 3+6=9.  8x9=72, so 7+2=9.  These numbers are partners on the nines river.  9x7=63 and 9x4=36 so 3 and 6 are partners.

Here is a picture of the river:

The rhyme from Grandma goes like this:
Take one away from the number with 9
Write that number down.
What's it's partner on the nines river?
Now your answer is found.

For example,  9 x 4 =
Take one away from 4. (3)
Write that number down.
What's it's partner on the nines river? (6)
Now your answer is found.

To remember the partners, my daughter made up this rhyme.
0 and 9 are the sun that shines.
8 and 1 are the anchor that hung.
7 and 2 are a scurvy crew.
6 and 3 are the waves of the sea.
4 and 5 keep the crew alive.

Zero is the sun and 9 is the clouds.  8 and 1 are an anchor.  7 and 2 are crew members.  4 and 5 are the sail.  6 and 3 are waves in the river.

My students love this rhyme and this picture.  I usually draw the picture by hand and have the students do the same thing, but my drawing looks awful so I made this one on the computer.  I also have my students write the facts out and we discover the fact that the partners total up to 9 together.  We practice finding the answers using the rhyme too.  Let me know what you all think of this!  I wish I could get a hold of Grandma's book.  I'm sure it is full of other great ideas too!

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