Whats the greatest whole number that uses all digits from 1 to 9

The greatest whole number using digits from 1 to 9, using the digits only once, is

987654321

Since our numeric system is positional, the digits further to the right are worth more than those to the left.

So, you want to assign a bigger coefficient to the digits which is more valuable in order to achieve the greatest number possible.

This means that the answer is simply 9876543210