Hi, this may be the wrong forum, but is there any math books that allow one to get better at advance mental math? IE how to square 91. You know the +/- 9 to get 100 and 82. Then 82 * 100 + 9^2 to get the answer of 8281. How to do math like that but easier or simpler because it is pretty complex to carry over numbers in your head.


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