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MathNet 2021 — Part 08 Question 58

Math Olympiad Vault · MathNet 2021 — Part 08

Question 58

The first COVID-19 infections in a care home were identified one week ago. Since then, the number of infected residents has increased fivefold, so it is now five times the number one week ago. This morning, $21$ of the infected residents were taken to hospital, leaving $9.\overline{09}\%$ of the residents remaining in the home infected. This evening, another $9$ infected residents will be taken to hospital, so only $5\%$ of the residents who remain will be infected. How many residents were infected one week ago, and how many residents were in the home in total at that time?