So  one third means you mutilply by 3  so 3x5 is 15 model cars
        
                    
             
        
        
        
Im pretty sure the correct answer is the fourth one
        
                    
             
        
        
        
Answer:
The correct answer is 
d. Sampling Interval = Population size ÷ Sample size.
Step-by-step explanation:
According to Johnstone et al., (2014) "<em>Once the auditor has determined the appropriate sample size, a sampling interval is calculated by dividing the population size by the sample size.</em>"
Thus,
Sampling Interval = Population size ÷ Sample size.
Johnstone, K., Rittenberg, L. and Gramling, A. (2014). <em>Auditing: A Risk-Based Approach to Conducting a Quality Audit.</em> Ninth Edition.