Aschool district decides to compare a new math textbook with the textbook that has been used for the past few years. each of the fourth graders in one school is randomly assigned to be in one of two classes, one in which a teacher continues using the old book and another in which a new teacher uses the new book. the school administrators compare the average scores of the two classes on a mathematics standardized test at the end of the year to determine which book is better.

The correct answer for the execise is that teachers have diferent amount of teaching experience and that is a potential confound in the study.

Explanation:

First of all, to conduct a comparison study to a certain dependent variable the researcher has to control all the conditions and only use the dependant condition as the different factor. However in our case, we have one major problem, the teachers should follow the same strategies, same classes, and practically do the same except the book employment. Because the teacher experience can affect the data, the study, the population, and the results. This research is potentially destined to be biased.

muslims have taken his goods and products to different parts of asia an indonesia. sometimes just traveled and trade, but in other occasions, stayed in the place and made a living.

trade was the key for muslims economies to prosper. their commerce routes reached far places like malaysia and java in the 11th century.

another important factor for prosperity was that muslim states served as the middle point for european traders.

they used to travel by land but sailing the seas -the indian ocean- really increase the exportation of products.