Teachers for several classes and a district are told to use a new method for teaching reading while all the other classes use traditional method at the end of the year a reading test is administered to see how well the students can read this is an example of what kind of statistical study

The correct answer is:

Experiment

Explanation:

In an experiment, one group is given a treatment while at least one other group is not.  After the treatment is finished, the results of the group that receive the treatment are compared with the results of the group (or groups) that do not receive the treatment, to determine if the treatment had any effect on the group.

In this problem, the different groups are the classes.  Some classes use the new method, which is the treatment, while other classes do not.  At the end of the year, the reading results of each class are compared to see if the treatment (new method) had any effect.

These are the multiples of 15 but what you are probably asking or what are the factors of 15