90
There are 200 positive four digit integers that have 1 as their first digit and 2 or 5 as their last digit. There are 9000 positive four digit numbers, 1000 through 9999. 1000 of them have 1 as the first digit, 1000 through 1999. 200 of them have 2 or 5 as their last digit, 1002, 1005, 1012, 1015, ... 1992, and 1995.
possibly than 20, 3040 3041 etc 3050 3051 etc
There are 320 such numbers.
A four digit whole number can be found from 1000 to 9999
Lowest four-digit number: 1000 Highest four-digit number: 9999
7000 - 999 ie 6001 four digit numbers
If the digits may be repeated, there are four choices for the first digit, four choices for the second, and four choices for the third. Thus there are 4x4x4 = 64 possible three-digit numbers with those digits. If the digits may not be repeated, there are still four choices for the first digit, but then only three remaining choices for the second, and then just two choices for the third. In this case there are only 4x3x2 = 24 possibilities.
2000.The smallest four-digit number there can be is 1000. So, add 1000 and 1000 to get 2000, then least sum you can get when adding two four-digit numbers.
900 numbers
There are 12 such numbers.
182
The four smallest three digit composite numbers are: 100, 102, 104, 105 with sum 411.