I was leafing through a book called "The Woman's Book: everything but the kitchen sink" by Francesca Beauman. It's been in my library for ages, and I occasionally flick through it.
It's one of these books that is, essentially, filled with completely random facts.
The random fact I came across was "The Marriage Formula".
Apparently, and I quote; "a simple mathematical formula exists to help one ascertain whether or not to accept a proposal of marriage."