Question

Four digits number can yo
u use twice

Answer 1

Answer:

largest four digit number=9999

smallest four digit number=1000

Answer 2

Answer:

repetitions are allowed, Two ways to get the answer: 1. There are 9999 integers starting with 1 and ending with 9999. But the 999 integers starting with 1 and ending with 999 have less than 4 digits, so the desired number is 9999-999 or 9000 ways.