I have a pleasant little feature story in the Monitor today about a Leap Day Baby born in Concord, which includes a little back-of-envelope calculation about how many such people live in New Hampshire:
Since there is one Feb. 29 every 1,461 days – with slight exceptions every few centuries, when things get messy to keep the calendar accurate – you might think there’s a 1-in-1,461 chance of being born on a leap day. But that’s not quite correct, because February is one of the slowest months of the year for births. The U.S. birth rate in late summer and early fall is about 8 percent higher than it is in mid-winter, so the odds of a leap day birth are actually more like 1,500 to 1.
Since there are about 1.4 million people in New Hampshire, that implies there are 933 leaplings living in the Granite State. Roughly.
Lots of handwaving there.
The only Leap Day baby I ever met was a student of mine years ago. I used to teach a probability class at BU and the first class of each semester I would start off with a probability example. I think it was called the Birthday Problem. Basically, it was that with certain assumptions the probability is such that with a group greater than about n = 22 the probability is greater than 50 percent that any two have the same birthday (not birth year). Then I would go around and ask each student one-by-one to state their birthdays. When I started, I noticed one woman’s face light up…..and sure enough when she stated her birthday, it was February 29th.