One mental math technique that I have shared with students is how to determine the product of nine multiplied by another number. This involves lowering one digit on one of their hands that corresponds to 9 x X. They then count the upright digits on either hand and superimpose the numbers together to find the answer. For instance, 9 x 7 would be 63 as 6 and 3 fingers are left on either side of the lowered digit. This technique is admittedly more simplistic than your listed mental math algorithms, but I think that it is still useful.
Andrew

Founder of https://mathtutorpro.com/

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