Hungry 9
Hungry 9
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133 comments
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Let's make that 9 a 10 because it's good enough, it's smart enough, and goshdarnit people like it. Also, I don't wanna add with a 9. So 10 + 7 would be 17, but we added 1 to the 9 to make it 10 so now we take 1 away, 17 - 1 = 16.
ezpz
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9 plus a number? No. 10 plus a number, minus 1. Yis.
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I just memorized any addition with 9 adds a 1 in front while reducing the other number by one. Same general step, but there's no 10 in my head, just 9+7 -> 16. Basically, promote the tens column while demoting the ones column. I think of it more like a mechanical scoreboard (flip one up, flip the other down) than an operation involving a 10.
If it's anything other than 9, I fall back to rote memorization, unless the number is big, in which case I'll do the rounding to a multiple/power of 10.
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Yeah that's a more accurate description of what i actually do in my head to. I'm not "adding 10", because I already would use a short hand method for adding 10 anyway to promoting the tens place or flipping the score card, as you said.
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133 comments