This week marks a very sad week for me and for many of the regular readers of this blog. A very dear friend – Girish Tutakne (popularly known as Tutu at IIT Delhi)- passed away in a very unfortunate accident in Melbourne a few days back. Girish was one of the most regular contributors to this blog along with both his sons. Today’s edition is being dedicated to Tutu, and I am republishing a puzzle that was contributed by him a few months back. Even after I knew the solution, I continued to be baffled by the answer, and I know many others felt the same way. It is one of the best puzzles posted on this blog.

Suppose we have 2 coins, with radii 2 cm and 6 cm respectively. The coin with the 2 cm radius is rotated on the circumference of the bigger coin. How many times will it rotate before it comes back to it’s starting point?

As always, please send your answers as comments within the blog (preferred), or send an e-mail to alokgoyal_2001@yahoo.com. Please do share the puzzle with others if you like, and please also send puzzles that you have come across that you think I can share in this blog.

My heart goes out to the Tutu’s family – Devika, Ayush and Ashish. I do hope to see future participation from all of them.