How many four digit numbers can be formed with the 10 digits 0, 1, 2, ..., 9 if no number can start with 0 and repetitio...

Question

How many four digit numbers can be formed with the 10 digits 0, 1, 2, ..., 9 if no number can start with 0 and repetitions are not allowed?

Accepted Answer

4536 We need four-digit numbers from digits {0,1,...,9} with no repeated digits and the leading digit cannot be 0. The leading digit has 9 choices (1-9); each subsequent digit is chosen from the remaining pool without replacement.