I remember learning my times tables in second grade. Mrs. Seivert handed out a mimeographed page with 1-10 in a row across the top and an identical column down the side, and what appeared to be random numbers in a chart below. Then, I memorized the table. Mission accomplished.
Yesterday, I volunteered in Cameron's Montessori kindergarten class. He was anxious to show me how he is learning multiplication and we he did show me, I understood why. It's fun. And you actually get to see how multiplication works.
He was working on his 8 times tables. For each number, there is a bar of beads -- the brown bars each have eight beads on them. So to figure out 8 x 9, Cameron would lay out nine brown bars and count the beads. But here's the amazing part. After he figured out that 8 x 9 is 72, he would then select 7 of the ten bars and 1 two bar to represent the answer. Genius!
By the way, the nine times tables were always my favorite because the answer sums to nine. 9 x 2 is 18, 1 + 8 is 9. 9 x 3 is 27, 2 + 7 is 9, and so on. I thought everyone loved this about the nine times tables, but then David told me he had never known that about them. So, I figured I'd share the nine times table love for anyone else out there unfortunate enough not to know that trick.
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3 comments:
Grandpa Miller taught me that trick. Some things never get old.
The nines trick is an extension of the general rule for the 3s times table - anything divisible by 3 will have the digits add up to 3, 6, or 9.
Interestingly, this is an artifact of our base 10 system. If we used, say, a base 5 system, it wouldn't work. However, the same trick would work for 4s. The 4 times table in base 5 runs:
4
13
22
31
40
and so on.
Or in the base 6 system, the 5s times table runs:
5
14
23
32
41
50
and on and on again.
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