Theory:

1. If the date of birth of Rahul is \(14/04/2005\), what is his age on \(04/02/2021\)?
 
Date of birth \(=\) \(12/04/2005\)
 
To find the age on date \(=\) \(09/02/2021\)
 
yy_mm_dd.png
 
Rahul's age on date \(09/02/2021\) is \(15\) years \(9\) months \(20\) days.
 
  
2. If \(15^{\text{th}}\) of August \(2020\) is Saturday, what is the day on \(10^{\text{th}}\) January \(2021\).
 
Solution:
 
Given: \(15^{\text{th}}\) of August \(2020\) is Saturday.
 
Number of days in August \(=\) \(31-14 =17\)
 
Number of days in September \(=\) \(30\)
 
Number of days in October \(=\) \(31\)
 
Number of days in November \(=\) \(30\)
 
Number of days in December \(=\) \(31\)
 
Number of days in January \(=\) \(10- 1 = 9\)
 
Total number of days \(=\) \(17 + 30 + 31 + 30 + 31 + 9 = 148\)
 
A week has \(7\) days.
 
So, divide \(148\) days by \(7\) days.
 
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\(148\) days \(=\) \(21\) weeks \(+\) \(1\) day
 
So, the required day is \(1\) day after Saturday.
 
Therefore, \(10^{\text{th}}\) January \(2021\) is Sunday.
 
Important!
If the remainder is:
 
\(0\) - Same given day
 
\(1\) - One day after the given day
 
\(2\) - Two days after the given day
 
\(3\) - Three days after the given day
 
\(4\) - Four days after the given day
 
\(5\) - Five days after the given day
 
\(6\) - Six days after the given day