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But to be clear -- the ability to do math in one's head while a good tool to have (even if just to get a date) is exactly the opposite of what I was saying.

I was thinking, you could also do 47 x 63 by taking out one of the factors of 63, say the 3 or the 7. For instance, 47 x 21 x 3, the first two are not hard to do in your head, 940 + 47 = 987, the multiply by 3. Using goofy's idea, that would be 3000, less the 3 x 13 that is in excess, giving you 2961.

Or you could do 47 x 9 x 7, again with goofy's method (works well with numbers close to 10, the first part is 470 - 47 = 423, then 423 x 7 is easier to do than 2 digits by 2 digits, essentially 2800 + 140 + 21 = 2961.

Regards, DTM
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