## Blue Eyes – a logic puzzle explained

After Tim Harford Tweeted the link to it, I spent a fair bit of time yesterday wrestling with what XKCD reckon to be

## The Hardest Logic Puzzle in the World

Here’s how it runs:

‘A group of people with assorted eye colors live on an island. They are all perfect logicians — if a conclusion can be logically deduced, they will do it instantly. No one knows the color of their eyes. Every night at midnight, a ferry stops at the island. Any islanders who have figured out the color of their own eyes then leave the island, and the rest stay. Everyone can see everyone else at all times and keeps a count of the number of people they see with each eye color (excluding themselves), but they cannot otherwise communicate. Everyone on the island knows all the rules in this paragraph.

On this island there are 100 blue-eyed people, 100 brown-eyed people, and the Guru (she happens to have green eyes). So any given blue-eyed person can see 100 people with brown eyes and 99 people with blue eyes (and one with green), but that does not tell him his own eye color; as far as he knows the totals could be 101 brown and 99 blue. Or 100 brown, 99 blue, and he could have red eyes.

The Guru is allowed to speak once (let’s say at noon), on one day in all their endless years on the island. Standing before the islanders, she says the following:

“I can see someone who has blue eyes.”

Who leaves the island, and on what night?’

Now, it’s possible to Google the answer but I thought it would be interesting the explain how I worked it out.

## Marrying Art and Digital with Interactivos!

Back in June I had the pleasure of helping out at Interactivos Birmingham. This was a fortnight-long workshop for people to develop projects that used?new technologies such as Raspberry Pi and Arduino to make art. In particular, these were pieces of art that responded to the world and people around them. The workshop was hosted and supported by Midland Arts Centre and run in partnership by Birmingham City University, Sampad, the BBC and Medialab Prado.

Nearly all of the projects that took part were using free and open software, and were also making the code that they wrote openly available for other people to see, contribute to and reuse. There is a set of repositories on Github for anybody who is interested in getting into the technical details of the projects.

What I really enjoyed about the workshop was the energy and enthusiasm that all of the participants brought with them. At the start of the fortnight I sat down with some of the project leads who, quite frankly, scared me with the scale of the projects they were hoping to deliver. While not everybody achieved all?they set out to do, each project achieved?lots in the relatively short time scales they had.

You can read all about the individual projects over at the Interactivos Birmingham website, which has loads of different content courtesy of Tim Wilson and BCU social media students.