Do you know leap year? There are 366 days in leap year. And when is leap year? Every 4 years, there is a leap year, this was what I learnt from school. And counting leap year, just divide current year by 4, right?
If so, then is 1900 a leap year? NO…
To get even closer to the actual number, every 100 years is not a leap year, but every 400 years is a leap year. Putting all of these rules together, you can see that a year is a leap year not only if it is divisible by 4 — it also has to be divisible by 400 if it is a centurial year. So 1700, 1800 and 1900 were not leap years, but 2000 was. That brings the average length of the year to 365.2425 days, which is even closer to the actual number.
I don’t know whether school teachers know this or not, because I was not taught about this.