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?
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The answer to last month’s riddle: 10, 13, 3, 12, and 2.
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See all riddles on http://blogs.exeter.ac.uk/xm2news/category/riddles/.