Dating someone with the same birthday
It’s like if I had a 1/10 chance of winning the lottery and I meet another person who also has a 1/10 chance of winning the lottery, then combined we have a 2/10 chance of winning the lottery.
If the details are precisely the same then they call them astro-twins. Other forms of the same construction are "astro twins," "astrology twins," and "star twins." days of her children.
So it will be $\approx$ P(Same year) $\times$ P(Same day).
For any one relationship, the odds of sharing the same month and day are approximately 1 in 365 (not exactly because of leap year and because births are not exactly evenly spaced within a year.
If there are 30 students in a class, there are 435 ways two students can be paired.
The odds of a “match” become 1/12 435/365…which is much greater than 100 percent.
Don't forget that them knowing they had the same birthday almost surely reflexively brought them closer together around the time they met.