Final answer:
The question is about the empirical rule for normal distribution, which indicates that the probability of a sample being within one standard deviation of the mean is 68%. Hence, the answer is a) 68%.
Step-by-step explanation:
The question pertains to the concept of normal distribution and the empirical rule (also known as the 68-95-99.7 rule). This rule suggests that for a normal distribution, approximately 68% of data falls within one standard deviation (±1SD) from the mean.
95% falls within two standard deviations (±2SD), and 99.7% falls within three standard deviations (±3SD). Given that we're looking for the probability that the number of cars that pass is within one standard deviation of the mean, we apply the empirical rule directly.
The probability that a sample falls within ±1SD of the mean in a normal distribution is approximately 68%. Therefore, the correct answer to the question is a) 68%.