3. How many natural numbers less than 10000 are there in whose decimal representation the digits 4, 8, and 9 do not appear, and the digit 1 appears exactly once? (The remaining digits can appear any number of times, including the possibility that they do not appear at all.)
3. The sought numbers are at most four-digit. If we pad each such number with leading zeros to a total of four digits (e.g., the number 17 would be written as 0017), then, since the digit 1 appears exactly once in the number, we have 4 positions to choose from for it, and for each of the remaining positions, there are 6 possibilities (all digits except $4,8,9$ and 1). Therefore, the number of sought numbers is $4 \cdot 6^{3}=864$.