A quality control manager wants to determine the percentage of defective light bulbs in the production line. Which of the following sampling methods would most likely lead to a valid inference?
A. testing every fiftieth light bulb in the production line
B. retesting 100 light bulbs that have already been tested
C. testing the last 4,000 bulbs in the production line
D. testing the first 2,000 light bulbs in the production line
A. testing every fiftieth light bulb in the production line
This method ensures a random sample of the light bulbs in the production line, which will help in obtaining a representative sample for determining the percentage of defective bulbs. The other methods may introduce bias into the sample, as they are not random or representative of the entire production line.