Riya may have any one of 365 days of the year as her birthday. Similarly, Kajal may have any one of 365days as her birthday.
A total number of ways in which Riya and Kajal may have their birthday are:
365 x 365
Then Riya and Kajal may have the same birthday on any one of 365 days.
Therefore the probability of Riya and Kajal may have same birthday are:
= 365/(365 x 365)
= 1/365