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My math book for my grade 3 DS as a strange way of doing Algerbra...or Pre algerbra as his teacher calls it...
So this is the example
N + 6 = 13
__  6(crossed out) = 6 (So its 613)
N = 7
Check 7+6 =13
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Quoting NYCitymomx3:
It's not strange. You subtract 6 from both sides of the equal sign to get N by itself (if the problem was N6=13, then you would ADD 6 to both sides). The 6s on the left cancel each other out (66=0 which is why it's crossed out on the left side of the equal sign). Now you have N=136 (or N=6+13) which =7. Oh, and it's algebra, not algerbra.
See that is just a clearer way then the teaching book said...thats tommrow...and thanks for the spelling correction I knew it looked wrong...

That is the way I was taught beginning algebra. It was explained that an algebra equation is like a balanced scale. Both sides are equal to each other. To maintain that balance, whatever you do to one side must also be done to the other side.
You want to end up with the unknown on one side of the equation,
N+6 = 13
N6 = 13 6 (moving the 6 from the left side to the right side)
N = 7
______________If the equation was as follows
N 6 = 13
N 6 +6= 13 + 6
N = 19
Check 19  6 = 13