A random selection of volunteers at a research institute has been exposed to a weak flu virus. After the volunteers began to have flu symptoms,

20

of them were given multivitamin tablets daily that contained

1

gram of vitamin C and

3

grams of various other vitamins and minerals. The remaining

20

volunteers were given tablets containing

4

grams of vitamin C only. For each individual, the length of time taken to recover from the flu was recorded. At the end of the experiment the following data were obtained.