Answer: 123456789
Explanation:
We need to write a 9-digit number using the digits 1, 2, 3, 4, 5, 6, 7, 8, and 9.
(where we can use each digit only one time)
We want the value of this 9-digit to be the smallest as possible, then:
The largest single value digit (9), needs to be in the smallest value place (in the units place)
The second larger digit (8), must be in the second smallest value place (in the tens)
And so on, then the 9-digit number will be something like:
123456789
Any other permutation will be larger than this number.