How many questions are there on a test if the numbered questions are 113 to 174? You must add one to account for the first question – subtraction will not give you the right answer. Here is the proof. Reduce the numbers to 1 to 5. If you subtract 5 – 1, you get 4, but there are 5 questions. You did not count number 1.
Consider an actual SAT question: 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. You must count customer 149.