Answer to Riddle 1 - Dentist's Problem

The boy was really the dentist's son and the dentist was really the boy's parent. The dentist was the boy's mother.

Answer to Riddle 2 - Face to Face

Any doorway will do. Place the sheet of newspaper in the doorway such that it is half at one side of the doorway and half is at the other side of the doorway. Close the door. Now two people can stand on the same sheet of newspaper, face to face, without touching each other.

Answer to Riddle 3 - Ping-Pong Problem

Fill the hole with water and the ball will float up.

Answer to Riddle 4 - Wetting Problem

Because he was bald.

Answer to Riddle 5 - A Running Man

It was a baseball game. The man was on third. The masked man was the catcher.

Answer to Riddle 6 - Sugar in Coffee is Dry

The woman put her sugar lump in dry coffee powder.

Answer to Riddle 7 - The Bear Problem

The bear was white.