50%
Three of them.
There are 21.
There are 20.
A bijective numeration is a numeral system which uses digits to establish a bijection between finite strings and the positive integers.
20. 16 without repeating a digit.
The sum of all the digits of all the positive integers that are less than 100 is 4,950.
279,999,720
Three of them.
They are 13.
405
There are 21.
52
There are none.
Every number from 100 to 999 inclusive !
3
The sum of the digits is 6.
81