Title text:
Other numbers are largely unaffected, but anyone using '4' for their certificate key is urged to upgrade to '5'.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3314/
I would really like to understand more, why do you simplify 320-0.520 as (3-0.5)*20? Is this system actually insightful into arithmetic? Is there a good tutorial about such and such?