> How often do you need to do arithmetic - multiplication, in particular - in a hurry with no aids? Every couple of minutes during my day I do some kind of men

> How often do you need to do arithmetic - multiplication, in particular - in a hurry with no aids? Every couple of minutes during my day I do some kind of mental calculation relating to my software development work. Anything from sense checking calculations when debugging, estimating file sizes/memory usage, worrying about when numeric overflow/underflow might be a problem. There are countless situations when being able to do quick calculations comes in handy. Of course I rarely multiply two numbers like 7x8 in isolation any more, but I am immensely grateful how Mrs El Guindi, my fifth grade teacher, drummed into us all fast, accurate mental arithmetic. Thanks to her, I can now look at a spreadsheet of numbers and immediately spot which ones are out of place.