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This problem belongs to the Contagious Maths: Understanding the Spread of Infectious Diseases collection.
If each person goes on to infect two others, how many generations would it take to infect...
Your school?
Your local community?
The nearest city to you?
Your country?
The whole world?
If you have an infected person, how many people do they go on to infect on average? As Julia explains, this is a very important question.
You can explore the effect of different values of R using this Desmos application.
In this video, Julia encourages us to consider the limitations of the model we have been using so far.
What assumptions did you need to make to work out your answers so far?
How realistic do you think they were?
This concludes Part 1. These resources continue with Part 2: Lucky Dip, the follow-up activity which introduces a more advanced model, and the concept of herd immunity.
In the "Teachers' Resources" section you will find suggestions as to how this material might be used in the classroom.
This is the first of four parts, designed to be used in a sequence of lessons - here is a lesson by lesson breakdown.
These Contagious Maths resources were developed and written by Julia Gog and the MMP team, including both NRICH and Plus, and funded by the Royal Society’s Rosalind Franklin Award 2020. We have tailored these resources for ages 11-14 on NRICH, and for older students and wider audiences on Plus.