Greetings, guzzlers.
As it’s Halloween this week...
The world has been overrun by zombies. None has come to Britain – yet.
The infectiousness of this year’s zombie virus, however, is well-known: an infected zombie has a 1/3 chance of passing the infection to a single human, a 1/3 chance of passing the infection to two humans, and a 1/3 chance of passing the infection to no one.
A single infected zombie arrives on the coast of Britain.
- What are the chances that the zombie outbreak will die out after two or fewer humans have become infected?
- What are the chances that the outbreak will die out by itself?
- How many people does a typical zombie infect on average?
- What’s spooky about the answers to the previous questions?
Clarifications: Once a human is infected he or she becomes a zombie. We can assume that Britain has is an unlimited supply of susceptible humans.
I’ll post the solutions on this blog later today. UPDATE: The solution post is now up.
Thanks to Adam Kucharski of the London School of Hygiene and Tropical Medicine for coming up with this question. Adam is a world expert on the spread of infectious diseases, like Ebola. He is also the author of the forthcoming book The Perfect Bet, out Spring next year.
I post a puzzle here on a Monday every two weeks. If you like this sort of thing check out my other Guardian blog Adventures in Numberland. You can also check me out on Twitter, Facebook, Google+ and my personal website.
If you like colouring for relaxation you might enjoy my latest book, Snowflake Seashell Star: Colouring Adventures in Numberland, which is out now.
And if know of any great puzzles that you would like me to set here, get in touch.
