The sum of all the digits of all the positive integers that are less than 100 is 4,950.
405
52
81
There are 20.
10*9*8=720
There are 870 such numbers.
There is only 1, the number 54.
The set of positive odd integers.
125
The sum of the first positive odd integers less than 101 is 10,000.
There are no positive integers less than any negative ones.
Positive integers are greater than zero. Negative integers are less than zero.