You get the largest number if you sort the digits, from largest to smallest.
Using the digits 12279, the largest number that can be represented is 97,221.
7654321
99
97432
If the digits are only used once, each, the largest possible number would be 97,531
The largest even number that can be made with those digits is 9740 .
The largest odd number that can be made with those digits is 9407 .
the largest five digit number that can be formed using the digits 7 and 9 is 97,000
543210
985,316
9650 is the largest formed by re-ordering the digits.