I apologize for what probably appears as a redundant thread. I actually did read through all the others, but there didn’t seem to be a consensus about which mental math system is best. I’m guessing this is because “best” really depends on what you’re hoping to achieve, so I’ll start there.
I’m looking for a system that allows for rapid multiplication of large numbers (maybe up to 4 x 4) and computation of square roots (and perhaps other fractional powers), and I’d like to do this without looking at written numbers for reference. I’d also (ideally) like the number to be produced from left to right, if possible.
I’m leaning towards Arthur Benjamin’s method (although I’ve never seen him compute square roots), but my concern is that I’ll invest 100 hours or so in one method just to find out that it’s deficient in one particular area, or an entirely different method is superior.
Does anybody know what system Granth Thakkar uses? I saw a video of him (or perhaps it was a similar competitor) doing 20 x 20 multiplication in his head. In the video, however, he looked at the numbers for reference, and he wrote down numbers as they were computed.
My suspicion is that one method may work best with smaller numbers (like 4 x 4) and lend itself more to rapid calculation without looking at written numbers, whereas another system–maybe like the one Granth Thakkar uses–may be better suited for longer calculations but would be inherently cumbersome without looking at numbers for reference.
Sorry for the long post. Any guidance at all would be greatly appreciated.