How many 10-digit numbers are there, such that the sum of the digits is divisible by 2?
I saw another forum with the same question, but the solution was to a different problem.
The first number =1,000,000,001
The last number =9,999,999,999
9,999,999,999 - 1,000,000,001 =8,999,999,998
8,999,999,998 / 2 + 1 =4,500,000,000 ten-digit numbers whose sum is divisible by 2.