That's still a bit slower than it needs to be. The real trick to doing something... | Hacker News

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		eachro on Jan 13, 2016 \| parent \| context \| favorite \| on: The Dying Art of Mental Math Tricks That's still a bit slower than it needs to be. The real trick to doing something like is seeing that we have 10(18x16) = 10(17^2 - 1) = 10(289-1) Having the first 30 squares committed to memory has been pretty useful for me.

bumbledraven on Jan 14, 2016 [–]

Right. And just to be explicit, we're using the fact that (x+1)(x-1) = x² -1. So to add in that step, it would be:

18 x 16 = (17+1)(17-1) = 10(17²-1)

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