How many days before vampires take over the world?

A vampire conundrum.

My latest book, Fly-Tipping, was published this week, so to promote it, this week's blog post is inspired by a question posed by one of the minor characters from the book:

"If a vampire drank the blood of one human per night, and every human he drank the blood of turned into a vampire who then subsequently also drank the blood of one human per night, how many days would it be before every person in the world was a vampire?”

Before I answer the question, here's a poll to see how many people get it right. Obviously I can't list every possible answer*, so instead I've grouped the answers into various ranges to make things a little easier.

* Well I suppose I could, but it would be a very long poll!


Scroll down the page for the answer...














The correct answer is actually 33 days, so well done to everyone who guessed less than 50 days. If you want to check the calculation for yourself, then every night each vampire bites one other person, so every night the number of vampires doubles. The number of vampires would therefore grow at the rate shown in the table below:

Table showing growth rate of vampires.

So after only 33 days there would theoretically be over 8 billion vampires, which is more vampires than there are people in the world! And yet somehow Buffy the Vampire Slayer managed to keep going for seven seasons! Top respect to Buffy's vampire slaying skills for keeping the impending vampire apocalypse at bay!

A vampire, pictured yesterday.

Of course in reality as more and more people got infected it would become harder for each vampire to find another human to infect. And of course also in reality vampires aren't real, so being fictitious would presumably make it even harder for vampires to infect people!

As I mentioned, two minor characters* from my latest book 'Fly-Tipping' discuss this very conundrum. They also discuss second hand Ghanaian underpants, so if you're interested in used underpants, or the growth rate of the vampire population, then why not check out Fly-Tipping at the link below!

* The minor characters are named Jags and Triviani.

You can find more statistically themed blog posts below:
Things that happen every second (part 2)
Micromorts: The risk of dying
Christmas statistics