Another puzzle I found on John Baez's blog. It seems to have been discovered and published only as recently as 2011. Baez's post gives a reference.
Two touching semi-circles, aligned as shown, are inscribed in a circle.
You might think you need more information, such as the relative sizes of the semi-circles perhaps. But in fact it doesn't make any difference.
I will post my solution on 6 March.
