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.