There are 28706 such combinations. 5456 of these comprise three 2-digit numbers, 19008 comprise two 2-digit numbers and two 1-digit numbers, 4158 comprise one 2-digit number and four 1-digit numbers and 84 comprise six 1-digit numbers.
Add the two greatest possible four digit numbers. 9999 + 9999
7
8100
250 of them.
There are 28706 such combinations. 5456 of these comprise three 2-digit numbers, 19008 comprise two 2-digit numbers and two 1-digit numbers, 4158 comprise one 2-digit number and four 1-digit numbers and 84 comprise six 1-digit numbers.
It is actually very simple, just take 10 to the square root of four. 10^4
There are 625 of them - too many to list.
Lowest four-digit number: 1000 Highest four-digit number: 9999
A four digit whole number can be found from 1000 to 9999
7000 - 999 ie 6001 four digit numbers
every number from 0000 to 9999
Any four-digit number that ends with 0, or with 5: 1000, 1005, 1010, 1015, ... 9990, 9995. If you want to have the complete list, I'll leave this fun part to you. Better write a computer program to list them.
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.
There are 360 of them.
900 numbers
There are 12 such numbers.