Record the numbers of grains of rice placed on a chessboard, up to 10 squares, and make a line graph. You can do this with the help of a spreadsheet.

If you are unsure how to do this, draw a pictogram or block graph for numbers up to 16 (the rice grains on just five squares of the chess board, as in the photograph).

One of the ways in which the spread of a disease is measured is by its reproduction number, known as ‘R’ (or ‘R0’). If a disease has an R number of one, this means that every infected person is likely to infect one more. If a disease has an R number of two, this means that every infected person is likely to infect two more. The spread of a disease with an R of two can be compared to the increasing number of grains of rice in the story.

It is also like being asked ‘Would you like a million coins now or a coin today, two tomorrow, four the next day and so on until the end of the month?’

This is sometimes called exponential growth. An exponent is the number of times a number is multiplied by itself. So, two people will each infect two more, who will each infect two more and so on. If this happened seven times then 2 to the power of 7 = 128 people would be infected.

As an extension activity, look up the R numbers of the pandemic diseases you have been learning about and add them to your display. You could draw a graph by hand, or by using the ‘people graph’ function in a spreadsheet, to compare R numbers from one to four after three weeks. This assumes that an infected person takes a week to become infectious and infect others and that no one has immunity to the disease.

**After three weeks **

**R1 3**

**R2 4**

**R3 9**

**R4 16**

You might want to watch a short video that simulates the spread of the H1N1 influenza pandemic of 1918–19, which started towards the end of the First World War.

You and other home learners in the UK or in other countries could share photographs of each of your displays, especially your Covid-19 cards and questions. You could discuss and vote on questions you exchange and this could lead to a shared project, drawing on information from both groups.