What's 19-1?

In an International Mathematics Competition...

QUESTION: Show that 19 - 1 = 20.

CHINESE: Do I look like a magician?

AMERICAN: You must be daydreaming!

JAPANESE: There's no common sense in this?

NIGERIAN: Simple! Simply write 19 in Roman Numerals and remove I to get 20.
That is, XIX - I = XX = 20.