What is the greatest and smallest 9-digit number using three different digits?
The greatest 9-digit number using three different digits is 999888777, formed by using the digits 9, 8, and 7 in descending order. The smallest 9-digit number using three different digits is 100000000, created with the digits 1, 0, and 0. This arrangement ensures that the number starts with 1, followed by the zeros to maintain the smallest value.