NO-ABEL 2007 Problem 1

We consider the sum of the digits of a positive integer. For example, the sum of the digits of $2007$ is equal to $9$ , since $2 + 0 + 0 + 7 = 9$ . (a) How many integers $n$ , where $0 < n < 100 000$ , have an even sum of digits? (b) How many integers $n$ , where $0 < n < 100 000$ , have a sum of digits that is less than or equal to $22$ ?