## Articles

What is herd immunity and what does it have to do with a number called *R*0?

How do mathematical models of COVID-19 work and should we believe them? We talk to an epidemiologist, who has been working flat out to inform the government, to find out more.

We look at a crafty mathematical device which, among other things, has helped people understand what causes cholera.

How should people arrange themselves for maximal socialising at a safe distance?

This puzzle is famous because the accepted answer is counter-intuitive. But is it always correct?

It's one of mathematics' most famous results: every "map" can be coloured using at most four colours. What it doesn't usually apply to, however, are real maps.

The golden ratio has many amazing properties. But is it really a secret of nature and the epitome of beauty?

Explore a mystery that intrigued Stephen Hawking until the end of his life.