C(n,r)=C(1000,3) = 166167000

you have 166.167m combinations.

This post has been edited by parkluyann1: Nov 8 2020, 02:42 PM

because we are talking about combination sets. For example we take three 3 digit numbers, 001 002 003.

001 002 003
001 003 002
002 001 003
002 003 001
003 001 002
003 002 001

These 6 arrangements are considered as 1 set because the numbers are repeating, albeit not in the same arrangement.

Combination sets does not take into account of number orders whereas Permutation does.