I picked up this trick intuitively as a very young kid, perhaps 7-8

I break multiplication and division up into chunks of 1's, 5's, and 10's so that it's mostly just adding a zero to the end, or doing that and then cutting it in half.

I never learned multiplication tables, long division, lattice multiplication or anything else. just did this in my head.

So say you want to find 86 * 32

86 * 10 = 860

860 * 3 = (2400 + 180 = 2580)

2580 + (86 * 2) = 2752

It starts to break down for bigger numbers depending on how "uneven" they are but it's been pretty useful in general