What is the smallest 5-digit number that can be formed using the digits 0, 1, 4, 6, and 9, where digits may repeat?

Question: What is the smallest 5-digit number that can be formed using the digits 0, 1, 4, 6, and 9, where digits may repeat?

Solution:
If we arrange the digits 0, 1, 4, 6, 9 in ascending order, we get the smallest number.

The smallest non-zero digit is 1.
Digits like 4, 6, 9 are larger than 1 and 0.

By using 1 once and 0 multiple times, the smallest 5-digit number that can be formed is = 10000.