Answer:
This is called a sample.
In statistics, we take a random 'sample' of people so that we can estimate values for the entire population!
So, say for example you want to find out what percent of students in your school are girls. You take a sample, like this again, of 30 students, and 3/10 are girls, then you can apply it to the rest of the population.
Hope this helps!
P.S. Stay Safe!
