Chess Story Explains Exponential Growth (COVID-19)


Both children and adults struggle to understand what the doubling of coronavirus disease (COVID-19) cases means. Doubling means exponential growth, which is explained in a memorable way by a famous chess legend. The King’s Chessboard by David Birch retells that legend.

Here is an example of how the number of COVID-19 cases might increase in your city. If the number of confirmed cases as of today in your city is 100, and there were only 50 cases in your city three days ago, then it took three days for the number of confirmed cases to double. Three days after today, perhaps the number of cases will double again, to 200 cases in your city. As long as cases are doubling at a constant rate, the growth is exponential.

Increasing the days to doubling means that health care workers and hospitals can keep up. For example, as hospitalized patients recover from COVID-19, they return home. Then their hospital beds are available for new patients. In the above example, what if it took 10 days (instead of three days) for cases to double from 100 to 200? Or 30 days before doubling? If the number of days to doubling can be increased even more, for example to 365 days, effective treatments might be widely available by then.

The King's Chessboard

Practice social distancing to slow the spread of COVID-19. When the disease spreads more slowly, it takes more days for the cases to double. Also, wash your hands with soap and water, for at least 20 seconds, “any time you enter from outdoors to indoors, before you eat, and before you spend time with people who are more vulnerable to the effects of COVID-19, including older adults and those with serious chronic medical conditions.”

A chess story, The King’s Chessboard, explains exponential growth. Here is a video of that story being read aloud. At the end of the video is homework from the teacher who posted the video. If you like, do the homework yourself or assign it to someone who likes chess-themed math problems. Post the answer to the problem in the comments to this article.

WIM Alexey Root, PhD

Alexey Root is a Woman International Master and the 1989 U.S. Women's chess champion. Her peak US Chess rating was 2260. She has a PhD in education from UCLA. You can find her books on chess on