Suppose two 20-year-olds wash up on a the desert island of Crusonia.  One is male, the other female.  They are both from the same country, but are otherwise randomly selected.  Both are convinced they have no hope of escaping the island.

Two questions:

1. What fraction of castaways pair bond over the next ten years?

2. If the castaways are unexpectedly rescued and return to their home country, what fraction of pair bonds remain together over the following ten years?

Please show your work.