They are abstract "word" problems, offered for the purpose of giving the student of high school mathematics valuable practice in the application and manipulation of the concept of "percent".
Often, some time spent in solving practice-examples such as these can lead to the phenomenon known as "learning", whereby the student comes to know, understand, and possess competence in a topic where he or she was previously ignorant and incompetent.
It is important to realize that the practice is the vital component in the process, whereas the answers alone have no value at all.
