Find the number of seven-digit numbers which can be formed with the sum of the digits being even.

There are 9000000 seven-digit numbers that exist. (Because the smallest 7 digit number is 1000000 greatest 7 digit number is 9999999

So total number of 7 digit numbers=9999999 – 1000000+1).

Out of 9000000 numbers, 4500000 are having the sum of digits as even and the remaining 4500000 are having the sum of digits as odd.

Every alternate number has its sum of digits even and odd.

There are 9000000 seven digit numbers.

So half of it is 4500000

So the required answer is 4500000.