If you mean 3-digit numbers whose digits are in decreasing order, then the answer is 20.
500 or so.
625 if numbers can have leading 0s, 500 otherwise.
500
There are 60 such numbers.
If you include the number 3,000, there are exactly 2,001 4-digit numbers between 500 and 3000.
400 of them.
The 3 digit numbers under 500 are 100 through 499.
9
1000 to 2999 inclusive so 2000 numbers.
If you mean 3-digit numbers whose digits are in decreasing order, then the answer is 20.
There are 156 such numbers.
500 or so.
625 if numbers can have leading 0s, 500 otherwise.
There are 6,750 such numbers.
500
110...... 500 to 599=100 405.415 till 495