What does "Well, I have a twenty, I’ll pay cash." mean in English for Spanish?

In English for Spanish, "Well, I have a twenty, I’ll pay cash." means:

Bueno, tengo uno de veinte, pagaré en efectivo.

Listen to "Well, I have a twenty, I’ll pay cash.": (If you have an HTML5 enabled browser, you can listen to the native audio below)

This is a phrase that is used in the GamesForLanguage English for Spanish Language Game in the following scenes:

• English for Spanish 3, Level 3, Scene 3