Answer:
What goes up and never comes down?
A grandmother, two mothers and two daughters went shopping together and everyone bought one purse each. How many purses did they bring home all together?
How do you discover something that does not exist?
4 rubber ducks were floating in the bathtub, 2 floated away and 2 drowned. How many ducks are still alive?
What can you fill a room with that takes up no space?
It is something you will never see again.