Choosing a group of 50 students from a roster of all students in a nearby school and inviting them to participate in a study would be an example of one way to?

It is one way to obtain a random sample.

Explanation:

As the name states, a random sample is a chosen group at random. A researcher tends to use random samples in order for his/her study to not be bias and avoid any other effects which are not wanted.

This example is clear; choosing a group of 50 students from a roster allows the individuals to be chosen at random and thus be a random sample.