Learning How to Count (Avoiding The Fencepost Problem)  Counting
isn’t easy. Suppose your boss wants you to work from 8am to
11am, and mop floors 8 to 11. Simple – it’s one floor per hour,
right?  Nope! There are 4 floors to mop (8, 9, 10 and 11) but
only 3 hours to work (8-9, 9-10, and 10-11).  Whoa — we count
floors and hours differently? You bet. And somehow, if the boss
said “Mop floors 8 to 11 on April 8th to 11th” everything would
be ok.  Today let’s unravel this counting mystery.  Basic
Counting  Numbers help us know “how many”. Take a numbered list
of houses:  There’s 52 houses there. Don’t count each one: the
addresses count for us! The numbers label the houses one by one,
just as we’d do. We can just read the last item: “1 to 52″ is 52
houses.     • Employee ID cards from 1 to 3493. There are 3493
employees.   • Days of the month from 1 to 31. There are 31 days
in that month.  What Does Subtraction Mean?  We often see
numbers as points on a line:  These points can be houses,
floors, or plain integer