Quick: What’s 99 + 47?
It’s 146. Of course it’s 146. You know how I know that?
Because I rounded the 99 to 100… and then subtracted one from 47 to make up the difference.
I sure as hell won’t do this:
That would be a waste of time when rearranging the numbers in your head is a lot faster. That’s what’s the math teacher in the video below is trying to explain to a news reporter using the numbers 9 and 6: