Final answer:
The sampling method being used is systematic sampling, where every 40th iPod is selected for testing and evaluation of performance.
Step-by-step explanation:
The sampling method being used in this case is systematic sampling. Systematic sampling is a method where every nth item in a population is selected for the sample. In this case, every 40th iPod is selected for testing and evaluation of performance. By selecting every 40th iPod, it ensures that the sample is representative of the entire population.