Question

How many 7-digit numbers are there in all?​

Answer 1

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.