TITLE: Why is it that if I count years from 2011 to 2014 as intervals I get 3 years, but if I count each year separately I get 4 years?
QUESTION [54 upvotes]: I'm not a very smart man. I'm trying to count how many years I've been working at my new job. I started in May 2011.
If I count the years separately, I get that I've worked 4 years - 2011 (year 1), 2012 (year 2), 2013 (year 3), 2014 (year 4).
But if I count the years as intervals, I get that I've worked 3 years 2011 to 2012 (year 1), 2012 to 2013 (year 2), 2013 to 2014 (year 3).
Have I worked 4 years or 3 years?

REPLY [4 votes]: When I studied Discrete Math at uni, they referred to this principle as "$1$ rope has $2$ ends".
The analogy in your example is a rope whose length is $3$ years, which has $4$ marks on it: