A Time Calculation Problem: 3yrs or 3yrs and 1 day? Suppose, a person A has his birthday on 30 Sept 1994 and another person B has his birthday on 30 Sept 1997, then which of the following statement would be correct and why? The difference between the ages of the two persons is 1. Three years correct to the number of Days 2. Three years and 1 day correct to the number of Days (because of 29th Feb 1996 that comes in between)?

You need to be precise about what you mean by a year, but in practise all alternatives will give you 1 as the correct answer.

Either you define a year so that it has constant length, for example 365.24 days, and then you observe that the difference between the two dates differs from 3 years with less than a day. This is the approach astronomers would take in their work.

Or you define a year so that it always has a whole number of days, like in the Julian or the Gregorian calendar. Then a year will not have constant length, which is messy when you work with astronomy, but is OK for most everyday purposes. Also in that case you get the same answer of 3 years, or Alternative 1.