How long is it from 1954 to 2013?

Answer 1

You must realize that you need to be a little more specific. How much of the two end years are you including? From January 1 1954 until December 31 2013 it is 60 years because you are counting each of the end years in full. From December 31 1954 to January 1 2013 it is 58 years and 2 days, because you are almost entirely eliminating the two end years.

From a person's birthday in 1954 until that person's birthday in 2013, the number of full years elapsed is 59; you are leaving out the the time before your birthday in 1954, and the time after it in 2013. These time periods combined will be one year.

The apparent confusion comes from the difference between calculating with discrete variables, and calculating with continuous variables. How many tickets do you have if you buy ticket number 5134, ticket number 5258, and all the tickets in order that are between them? The answer is 25, not 24. Tickets are discrete variables; you subtract and then add 1 to the difference. It is easy to see if you have only tickets numbered 5134 and 5135. You clearly have two tickets, but subtracting their numbers gives you a difference of one.

Generally we can think of years as being closer to continuous variables and not discrete. Think of individual dates in the year as being analogous to points on the number line. This is not exactly accurate, but analogous, and close enough for calculating age. From a birthday in one year to that person's birthday in another year, you simply subtract the smaller numbered year from the larger one to get the number of elapsed years.