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I highly recommend the Secrets of Mental Math book: http://a.co/095nXaa http://a.co/095nXaa Lots of good insights on how to make shortcut mental calculations.
by tzhenghao 9y ago
I highly recommend the Secrets of Mental Math book:
http://a.co/095nXaa http://a.co/095nXaa
Lots of good insights on how to make shortcut mental calculations.