Pick 4 different numerals from 0 - 9 and arrange them to make the largest possible number.		for example: 8732
Now arrange the same numerals to make the smallest possible number.		2378
Subtract the smaller number from the larger.		8732-2378=6354
Arrange the numerals in the answer to make the largest and smallest possible numbers, and subtract those numbers.		6543-3456=3087
Continue with this process until you end up with 6174.		8730-378=8352 8532-2358=6174!

Does it always work? Try 4 new numerals and see if you can end at 6174 every time!