Step 1 :Given the weights of the cars in hundreds of pounds as [27, 32, 34, 35, 32, 30] and the fuel efficiency in miles per gallon as [24, 23, 18, 21, 25, 21].
Step 2 :The correlation coefficient is a measure of the strength and direction of the relationship between two variables. It ranges from -1 to 1, where -1 indicates a strong negative relationship, 1 indicates a strong positive relationship, and 0 indicates no relationship.
Step 3 :Calculate the correlation coefficient between the weight of a car and the fuel efficiency.
Step 4 :The correlation coefficient between the weight of a car and the fuel efficiency is calculated to be -0.5224303472635711.
Step 5 :Round the correlation coefficient to three decimal places.
Step 6 :Final Answer: The correlation coefficient between the weight of a car and the fuel efficiency is \( \boxed{-0.522} \).