1. Since half of the 97% wear two earrings and the other half don't wear a single earring it is as if every single one of them wears one earring. And since the other 3% of the women really wear one earring each the total number of earrings is 800.
2. Since there were only two barbers they must have cut each other's hair. The second must have his hair cut by the first!
3. He had already put sugar in his coffee before he noticed the fly!
4. They are triplets.
5. There were only three persons at the table comprising a grandfather, his son and his grandson.
6. Mount Everest, of course. It was always there!
7. In a dictionary.
8. Three.
9. A leaf.
10. Put yourself back to back of each other.
11. An echo.
12. It happened during the daytime!
13. He was in a merry-go-round.