It has 5 digits. There is a 4 in the ten thousands place. None of the other digits is a 4. What is the smallest number that this mystery number can be?
We first consider the lowest number that can be used to get the mystery number. Since we can not use 0 since if we put 0 before 4,000, it will only have 4 digits. So we use 1. Now we have 14000.
