There are 10 digits in total (0, 1, 2,...,9).

Two digits are in use already.

Since no digit is used more than once, we have the following:

For the 3rd digit, there are 10-2=8 choices.

For the 4th digit, there are 10-3=7 choices.

For the 5th digit, there are 10-4=6 choices.

Thus the total number of outcomes is 8*7*6=336