Answer:
Answer is even on the 11th turn unless Slowhan is allowed to skip a turn.
Explanation:
If you add or subtract every turn then every turn will always be the opposite of the last turn, so, it would be.
odd is 0
1 = even
2 = odd (You've seen here that every even numbers of turns how answer will be odd and when it is an odd number of turns it will be even)
3 = even
4 = odd
5 = even
6 = odd
7 = even
8 = odd
9 = even
10 = odd
11 = even