Even in an age of smartphones, crunching numbers quickly — and getting good at it — can give you snappy, useful answers to pressing real-life math questions such as, Is this shirt a good deal? or How much should I tip my Uber driver? Here are some good mental math shortcuts to keep under your hat.
from https://www.apartmenttherapy.com/everyday-math-shortcuts-to-memorize-254594
from waaaay over here —> 9 Secret Shortcuts of People Who Are Good at Everyday Math
from Sofia Consola
via 9 Secret Shortcuts of People Who Are Good at Everyday Math
