Correct Answer - Option 4 : Cannot be determined
Sadashiv remembers that Sanjay’s birthday is certainly after January 12 but not later than January 16.
Clearly, Sanjay’s birthday falls on 13th, 14th or 15th.
If Meher remembers that Sanjay’s birthday is before January 17 but not before January 13,
Clearly, Sanjay’s birthday falls on 13th, 14th,15th or 16th.
From both the statements, we get:
Sanjay’s birthday falls on 13th, 14th or 15th.
There are three possible dates for Sanjay’s birthday.
So, it cannot be determined on which date is Sanjay's birthday.
Hence, ‘Cannot be determined’ is the correct answer.