Answer:
900,900 outcomes are possible.
Step-by-step explanation:
Arrangements with repetition:
The number of possible arrangements of n elements, considered that they are divided in classes of
elements, is given by:

A dancing competition has 13 competitors
This means that 
Four are American, two are Mexicans, four are Russians and three are Italians.
This means that 
How many outcomes are possible?

900,900 outcomes are possible.