I think the answer is 23.
Here are some logical puzzles:
1. What can be full of water and full of holes at at the same time?
2. In a game of chess, how many different choices do you have for your first move?
3. It's been around for millions of years, but it's no more than a month old. What is it?
4. Lizzie is 16 years younger than Joanna. In 10 years time Joanna will be twice as old as Lizzie. How old are they now?
5. What are the next four letters in this series.
Y Y H L Y E Y T ...
6. ENUMERATION is an anagram of which other 11 character word in the English language?
7. Can you decode the following to find a hidden message? You've probably got a tool to do so with you now.
Q5A6Q3 A1Z6A2Q2Q3Q4 Q8A2 A1Q5 Q6Q9Q7Q4 A4Q8Z6AGQ3Q4Q5Q8Q10A2
8. What gets wetter and wetter the more it dries?
9. What time is it when the number of minutes since midnight is nine times the number of minutes before noon?
And the last: How many black circles can you see in the image below?