Why do you add +1 in counting test questions? Here's an example question from the SAT question of the day:

On the last day of a one-week sale, customers numbered 149 through 201 were waited on. How many customers were waited on that day?
  Possible answers: 51, 52, 53, 152, 153.

The correct answer here is 53, which is the result of (201-149) + 1 = 53.
What's the reasoning in adding the +1?

You have to think, is it inclusive or exclusive.  If inclusive then it includes 149 AND 201.  Therefore the answer is 201 minus (1 less than 149) == 201 - 148.
Using algebra:
a ... b inclusive

== b - (a-1) == b - a + 1

So there you have your +1
