Imagine you used a numeric keypad to type out all the integers from $1$ to $10,000$ (inclusive). What is the result when you subtract the digit on the keypad used least often from the digit on the keypad used most often (most minus least)?
First note that each of the digits $1,2,\ldots,9$ occur the same number of times by symmetry if we count up to $10,000$ exclusive. We note that since $0$ doesn't appear as the first digit it must appear the least number of times. Thus, since $10,000$ contains $1$, the digit $1$ occurs most often and $0$ occurs least often giving an answer of $1-0 = 1$.