11. How many integers between 1 and 2005 (inclusive) have an odd number of even digits?
11. The answer is 1002. If the unit digit of an integer $n$ is even, then the unit digit of $n+1$ is odd, while all other digits of $n$ and $n+1$ are the same. Therefore, if $n$ has an even number of even digits, then $n+1$ has an odd number; and if $n$ has an odd number of even digits, then $n+1$ has an even number. Thus, exactly one of $n$ and $n+1$ has an odd number of even digits. By dividing the integers from 2 to 2005 into the 1002 pairs $(2,3),(4,5),(6,7), \ldots,(2004,2005)$, it follows that exactly 1002 of them have an odd number of even digits. Since 1 has no even digits and thus should not be counted, the answer is 1002.