## The mathematics of lockdowns

During the pandemic the death rate per 100,000 of population has varied widely between countries. For example at the time of writing the UK's rate is 72.51 while Germany's is 13.40, a factor of 5 smaller despite the two countries being superficially similar in other ways (https://en.wikipedia.org/wiki/COVID-19_pandemic_death_rates_by_country, snapshot at time of writing: https://en.wikipedia.org/w/index.php?title=COVID-19_pandemic_death_rates_by_country&oldid=985851183).

There are obviously many things that the UK and Germany did differently but the media have particularly focused on the fact that Germany locked down earlier than the UK. Coronavirus was first confirmed in Germany on January 27 and they locked down on March 13, a period of 46 days, whereas the first two cases in the UK were confirmed on January 31 and lockdown began on March 23, a period of 52 days, six days later than in Germany.

This doesn't seem like a huge difference. Could it really be that locking down a mere six days earlier could have reduced the UK's death rate by four fifths? This article attempts to answer this question. To do so requires only simple school-level maths.