A scientist investigated the effect of an antibiotic on the treatment of cholera. 320 people suffering with cholera were split into two groups. One group was treated with an antibiotic while the other group was not given antibiotics. Both groups were given fluids containing sugars and mineral salts (oral rehydration therapy). The scientist recorded the number of days that each person suffered from diarrhoea. The table shows the results. [Figure 38.1 - table of mean time suffering from diarrhoea for different treatments] What is the percentage decrease in the mean time that a person suffered from diarrhoea when they were treated with the antibiotic?

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