How to add 6 to 9
They said the kids were never taught WHY. OK, that is fair. There is a LOT of stuff I never found out ****WHY****! DECADES later, even with the internet, I STILL don't know WHY. Does ANYONE? I DOUBT IT!
OK, fair enough. It is the SIMPLEST concept in common core that I have seen explained in the simplest way. I could do it in a more flexible way than they did in LESS time! HECK, I could use the extra time to teach the ENTIRE TIMES TABLE for nine up to TEN! Want to see? OK!
We use base ten, so if a given position goes past 9 it changes to zero, and flips the next number:
1-9
10
11-19
20
...
91-99
100
SO 9+6 could be expressed as 16-1, or 15! 9+1 is 10, of course, 9+2=11, etc...
OK, done teaching y9+x!
With times tables? Anything times 0=0 Anything times 1= the other number, so 15x1=15.
2 to 9 could be expressed as (9-y) for the tens followed by y where y=10-x
9*2=18 x=2 y=8 (9-8)=1 y=8
9*8=72 x=8 y=2 (9-2)=7 y=2
9*9=81 x=9 y=1 (9-1)=8 y=1
That's all the times tables for 9. Once you recognize the pattern, it is simple and quick.
NOW, WHY is 10+5=15? You just have to try it out and convince yourself. WHY is 9*9=81? DITTO!
Why do most healthy people have ten fingers and ten toes? In my defense, THEY never answered those questions EITHER!
Steve
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