To answer this question, let's consider the given information: Joe was both the 5th highest and 5th lowest in a race.
This means that Joe finished in the 5th position from the top and the 5th position from the bottom.
Let's analyze the options to determine the number of participants:
Option A) 10 - If there were 10 participants, then Joe being the 5th highest and 5th lowest would be possible. This option is a possible answer.
Option B) 9 - If there were 9 participants, then Joe being the 5th highest and 5th lowest would be possible. This option is a possible answer.
Option C) 11 - If there were 11 participants, then Joe being the 5th highest and 5th lowest would not be possible. This option is incorrect.
Option D) Don't Know - This option does not provide a specific answer and cannot be considered correct.
Therefore, the correct answer is B) 9. There were 9 participants in the race.