Using the digits $0$,$1$,$2$ and $4$, find the sum of all four-digit numbers that can be formed. Repetitions not allowed.
total number of $4$-digit numbers that can be formed $= 3 \cdot 3 \cdot 2 \cdot 1 = 18$ numbers.
Total number of times each digit appears$= 18/4=4.5=4$ times. But answer is wrong, although my approach of doing it isn't wrong I feel. What mistake am I doing in finding the number of times each digit appears?