In need of a break? Try and figure this one out for a bit of a change:
One to six is what is there. All you can see though is fifteen to twenty, as well as five, but never twenty-one, unless it’s in the air. What is it?
The answer to last month’s riddle: 10, 13, 3, 12, and 2.
See all riddles on http://blogs.exeter.ac.uk/xm2news/category/riddles/.