Use the Following Information to Answer Questions (5) - (7)

Use the following information to answer questions (5) - (7) . A tire manufacturer has made some
modifications to its most popular tire and wants to see if the tread on the modified tire will last
longer than the original tire. Because there is much variation in the way people drive, the
manufacturer decides to use blocking to reduce this variation. Twenty cars will be used to test the
tires. Ten cars are randomly selected to receive an original tire on the right rear wheel and a
modified tire on the left rear wheel. The remaining ten cars will receive an original tire on the left
rear wheel and a modified tire on the right rear wheel. Each car will then be driven 10,000 miles and
the amount of wear recorded for each wheel.
-Was the study described above most likely an observational study or a controlled experiment?

A) Experimental because the researchers placed both types of tires on each car, randomly assigning one type of tire to the right side and the other type to the left side.
B) Experimental because the researcher could not control how fast each car was driven.
C) Observational study because the researcher decided which car received which type of tire.
D) Observational study because the tires were not a random sample.