As you can see, 4 of the 24 students don't partecipate in any activity. This clearly implies a ratio of 4:24, or 1:6.
We could infer that this ratio holds for the whole school, or even for all the boys and girls of that age.
That's the point of surveys and inferring: you gather data about a relatively small group, and then assume that the proportions you have are valid for a much larger group.
That's why it is important that the group that you survey is balanced and unbiased.
